# How to combine PHP and interest? (New task)

Please help me solve a small problem with percentages+ PHP 🙂

``````<?php
\$x = 100; //  ""   100
\$y = \$x - 10%; //  "Y"  ,   100  10%
echo \$y;    //
?>
``````

If everything was so easy, then the variable “Y” was assigned the number 90, but it gives an error in the browser 🙁 I understand that I wrote the task incorrectly. Please help and show how to correctly write tasks with percentages in PHP code.

Thanks in advance. AronTito

Complicate the problem Einsteins

``````<?php
\$X = 1536.56;
\$Z = \$X - 11.5%;
echo \$Z //    ???
?>
``````

## Answer 1, authority 100%

Sort of simple:

``````<?php
\$x = 100;
\$y = \$x * ( 100 - 10 ) / 100; // 100%   10%
//  100
// :
\$y = 0.9 * \$x;
echo \$y;
?>
``````

## Answer 2, authority 100%

Learn materiel, and not even php, but 5th grade matan

``````\$x = 100; //  ""   100
\$y = \$x * 0.9; // ,  , \$x * (100-10)*0.01  \$x - \$x*(10)*0.01
``````

## Answer 3, authority 50%

A percentage is (by definition) a hundredth. There are no percentages in PHP as such. The `%`character serves other purposes.

Whenever you work with percentages (subtract as in your case) – work with hundredths (fractions) of numbers.

If you need to subtract 10 percent, it just means that you need to subtract 10 hundredths. 10 times 1/100. The x in your question acts as the original number. And its percentage is a hundredth of it, `x/100`. 10 percent of x is ten such shares `(x/100) * 10`.

Thus, an entry like `y = x - 10%`becomes:

``````y = x - ((x / 100) * 10)
``````

How many percent you want to subtract (or add or do whatever), enter that much at the end of the expression.

Yes, just everything!

Subtract 10% from 100:

``````<?php
\$x = 100;
\$y = \$x * 0.9;
echo \$y;
?>
``````

Subtract 11.5% from 1536.56:

``````<?php
\$x = 1536.56;
\$y = \$x * 0.885;
echo \$y;
?>
``````

``````<?