Useful Tips

How to calculate percentages: from a number, from the sum of numbers, etc.


So you will find the numerical equivalent of 1%. Then it all depends on your goal. To calculate the percent of the amount, multiply them by the size of 1%. To convert the number to percent, divide it by 1%.

You go to the supermarket and see a promotion for coffee. Its usual price is 458 rubles, now there is a 7% discount. But you have a store card, and on it a pack will cost 417 rubles.

To understand which option is more profitable, you need to convert 7% to rubles.

Divide 458 by 100. To do this, simply shift the comma separating the integer part of the number from the fractional one by two positions to the left. 1% is 4.58 rubles.

Multiply 4.58 by 7, and you get 32.06 rubles.

Now it remains to subtract 32.06 rubles from the usual price. On the stock coffee will cost 425.94 rubles. So, it’s more profitable to buy it on the map.

You see that the game on Steam costs 1,000 rubles, although it used to be sold for 1,500 rubles. You are wondering how much the discount was.

Divide 1,500 by 100. Moving the comma to two positions to the left, you get 15. This is 1% of the old price.

Now divide the new price by 1%. 1,000 / 15 = 66.6666%.

100% - 66.6666% = 33.3333%. Such a discount was provided by the store.

2. How to calculate the percentage by dividing the number by 10

This method is similar to the previous one, but counting with it is much faster. But only when it comes to percentages that are multiples of five.

First you find the size of 10%, and then divide or multiply it to get the right amount of interest.

Suppose you deposit 530 thousand rubles for 12 months. The interest rate is 5%, capitalization is not provided. You want to know how much money you will take in a year.

First of all, you need to calculate 10% of the amount. Divide it by 10 by moving the comma to the left by one character. You will get 53 thousand.

To find out how much is 5%, divide the result by 2. This is 26.5 thousand.

If in the example we were talking about 30%, you would need to multiply 53 by 3. To calculate 25%, you would have to multiply 53 by 2 and add 26.5.

In any case, using such large numbers is quite simple.

3. How to calculate the interest, making a proportion

Composing proportions is one of the most useful skills taught at school. With it, you can calculate any percentage. The proportion looks like this:

amount of 100%: 100% = part of the amount: percentage.

Or you can write it like this: a: b = c: d.

Usually the proportion reads as “a refers to b in the same way as c refers to d”. The product of the extreme members of the proportion is equal to the product of its middle members. To find out an unknown number from this equality, we need to solve the simplest equation.

For an example of calculations, we use a quick brownie recipe. You want to cook it and bought a suitable bar of chocolate weighing 90 g, but could not resist and bit off a piece or two. Now you have only 70 g of chocolate, and you need to find out how much butter to put instead of 200 g.

First, we calculate the percentage of remaining chocolate.

90 g: 100% = 70 g: X, where X is the mass of the remaining chocolate.

X = 70 × 100/90 = 77.7%.

Now we make a proportion to find out how much oil we need:

200 g: 100% = X: 77.7%, where X is the right amount of oil.

X = 77.7 × 200/100 = 155.4.

Therefore, about 155 g of butter should be put in the dough.

The proportion is also suitable for calculating the profitability of discounts. For example, you see a blouse for 1,499 rubles with a 13% discount.

First, find out how much a blouse costs as a percentage. To do this, subtract 13 from 100 and get 87%.

Make a proportion: 1 499: 100 = X: 87.

X = 87 × 1,499 / 100.

Pay 1 304.13 rubles and wear a blouse with pleasure.

4. How to calculate interest using ratios

In some cases, you can use simple fractions. For example, 10% is 1/10 of the number. And to find out how much it will be in numbers, it is enough to divide the whole by 10.

  • 20% - 1/5, that is, you need to divide the number by 5,
  • 25% — 1/4,
  • 50% — 1/2,
  • 12,5% — 1/8,
  • 75% is 3/4. So, you have to divide the number by 4 and multiply by 3.

You found pants for 2,300 rubles with a 25% discount, but you only have 2,000 rubles in your wallet. To find out if there is enough money for a new thing, do a series of simple calculations:

100% - 25% = 75% - the cost of trousers as a percentage of the original price after applying the discount.

2,400 / 4 × 3 = 1,800. That is how many rubles are pants.

5. How to calculate interest using a calculator

If life isn’t nice without a calculator, all the calculations can be done with it. And you can do even easier.

  • To calculate the percentage of the amount, enter a number equal to 100%, a multiplication sign, then the desired percentage and a% sign. For an example with coffee, the calculations will look like this: 458 × 7%.
  • To find out the amount minus interest, enter a number equal to 100%, minus, percentage and sign%: 458 - 7%.
  • Similarly, you can add, as in the example with a deposit: 530,000 + 5%.

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Option 1: calculation of primes in the mind in 2-3 seconds.

In the vast majority of cases in life, you need to quickly figure out in your mind how much it will be a discount of 10% of a certain number (for example). Agree, in order to make a purchasing decision, you do not need to calculate everything down to the penny (it is important to figure out the order).

The most common options for numbers with percentages are listed in the list below, as well as what you need to divide the number in order to find the desired value.

  • 1% of the number = divide the number by 100 (1% of 200 = 200/100 = 2),
  • 10% of the number = divide the number by 10 (10% of 200 = 200/10 = 20),
  • 25% of the number = divide the number by 4 or two times by 2 (25% of 200 = 200/4 = 50),
  • 33% of the number ≈ divide the number by 3,
  • 50% of the number = divide the number by 2.

The challenge! For example, you want to buy equipment for 197 thousand rubles. The store makes a discount of 10.99% if you fulfill any conditions. How quickly can I figure it out, is it worth it?

An example of a solution. Yes, just round off these pair of numbers: instead of 197, take the amount of 200, instead of 10.99%, take 10% (conditionally). In total, you need to divide 200 by 10 - i.e. we estimated the size of the discount at about 20 thousand rubles. (with some experience, the calculation is done almost on the machine for 2-3 seconds.).

Exact calculation: 197 * 10.99 / 100 = 21.65 thousand rubles.

Option 2: use Android phone calculator

When the result is needed more accurate, you can use the calculator on the phone (in the article below I will give screenshots from Android). Using it is quite simple.

For example, you need to find 30% of the number 900. How to do this?

Yes, quite simple:

  • open the calculator
  • to write 30%900 (naturally, percent and number can be excellent)
  • note that below under your written "equation" you will see the number 270 - this is 30% of 900.

Below is a more complex example. Found 17.39% of the number 393 675 (result 68460, 08).

one more example

If you need, for example, to take 10% from 30,000 and find out how much it will be, then you can write it like that (by the way, 10% of 30,000 is 3,000). Thus, if you subtract 3,000 from 30,000, there will be 27,000 (as the calculator showed).

Subtract 10% from the number (another example)

In general, a very convenient tool when you need to calculate 2-3 numbers and get accurate results, up to tenths / hundredths.

Option 3: consider the percentage of the number (the essence of the calculation + the golden rule)

It is not always and not everywhere that you can round numbers and calculate percentages in your mind. Moreover, sometimes it is required not only to get some exact result, but also to understand the very "essence of the calculation" (for example, to calculate a hundred / thousand different tasks in Excel).

In these cases, I recommend remembering one golden rule of the column. If you understand it, then without problems you can always solve problems with interest. So.

Suppose we need to find 17.39% of the number 393,675. Let us solve this simple problem.

  1. first write down the number 393675 on the piece of paper and write 100% opposite it (i.e., the number we are trying to find a percentage of - we consider it as 100%),
  2. then write under 100%, the percentage that you want to find (i.e., 17.39 in our example), under the number itself - put "X" (that is, the number you need to find, see the screen below) . Here the main number is to write under the number, percent under the percentage (and do not confuse them)!

We write down the numbers for calculating interest

Now see how easy it is to find X: it’s enough to multiply the original number with the desired percentage (diagonal rule: where two numbers are known - multiply them) and divide by 100. See the screen below. You can multiply it on a calculator (business for 10-15 seconds).

Cross to cross (count percentages)

To remove all points on "I", I consider the inverse problem. For example, how many percent is the number 30,000 of the number 393,675.

  1. first we write down a column also 393 675 and in front of it we put 100%,
  2. Next, under the number 393 675 itself, we write 30,000, and in front of it we put X (i.e. what we need to find),
  3. further (30,000 * 100) / 393675 and we get 7.62% (you can check). Those. The rule also works: we multiply the cross by the cross (that is, where two numbers are known on the diagonal) and divide by the rest. Thus, it is easy to find the unknown.

Percentage Inverse Problem

Option 4: calculate interest in Excel

Excel is good because it allows you to make quite voluminous calculations: you can simultaneously calculate dozens of very different tables, linking them together. Anyway, unless you manually calculate the interest for dozens of items, for example.

Below I will show a couple of examples that you most often encounter.

The first task. There are two numbers, for example, the purchase and sale price. You need to find out the difference between these two numbers in percent (how much one is larger / smaller than the other).

  1. First, we arrange all this in Excel in the form of a tablet (see the example below: in my case, we will calculate the interest for the “Margin” column by the purchase price and the sale price of the product),

How to determine how much one number is greater than another in percent

further, just in case, I’ll remind you how to find out how many percent one number is from another (for example, I took the first line from the table above). According to a simple “rule” (described a little earlier in the article), we get that the difference between these numbers is 4.36%. See screen below.

The second number is 104% of the first

Now it remains to write this formula in Excel: = (C2 / B2) * 100 - 100 (see screen below). The problem for the first row is solved - the difference between the purchase price and the sale price is 4.36%.

in order to calculate the percentages for all other lines - just stretch the formula (see screen below).

The formula was stretched - percent calculated for the entire column

For a more accurate understanding, I will give one more example. Another problem: there is the purchase price and the desired percentage of profit (say 10%). How to find out the selling price. Everything seems to be simple, but many "stumble".

  1. first we also open Excel and enter the data in a tablet,

For what price to sell if you need a margin of 10%

then we need to find 10% of the purchase price (i.e. the number by which we need to increase the purchase price). To do this for the first row of the table, all according to the same rule (see screen below), you need: (3737 * 10) / 100 = 373.7

We consider how much one number is greater than another in percent

Now you can draw up the formula for the first row in Excel: = (B2 * D2) / 100 + B2 (see screen below). Those. First, we found how much 10% of the purchase price will be, and then we added the purchase price to this number. Everything seems to be simple and logical.

We write the formula for our problem

Well, the last touch: just stretch the formula to the rest of the lines. The problem is solved!

Stretch the formula - the problem is solved

Additions on the topic are always welcome.

Which rule applies

This verb contains the alternating even / chet root. The choice of a vowel in it depends on whether the word has the suffix "a". If it is, then select the root "cheat", if not, then - "even". Compare: deduction - count. As you can see, in the presented word there is an affix “a”, therefore we write the verb with “and”. It is worth remembering that this root has homonyms. If the emphasis in the word falls on the prefix “you”, then we are dealing with a lexeme formed from the verb “read”. And then we check the root vowel by stress. As a verification token, we use, for example, the noun "read".

Subtract a column from numbers containing zeros.

Again, let’s look at an example:

We write numbers in a column. Which is more - on top. We start the subtraction from right to left one digit at a time. 9 - 3 = 6.

Subtract 2 from zero does not work, then again we occupy the numbers on the left. This is zero. We put a dot over zero. And again, it will not work at zero, then we move on to the next digit. We borrow from a unit. We put an end to it.

Note: when there is a dot in the subtraction with a column above 0, zero becomes nine.

There is a point above our zero, which means it has become a nine. Subtract 4 from it. 9 - 4 = 5. There is a dot above the unit, that is, it decreases by 1. 1 - 1 = 0. The resulting zero does not need to be written.