How to minus a percentage in python

The simplest way to "subtract 20%" involves no subtraction at all:

>>> x = 10
>>> x *= 0.8          # shorthand for x = x * 0.8
>>> x
8.0

But if for whatever reason you wanted to actually subtract something, here's how:

>>> x = 10
>>> x -= (x * 0.2)    # shorthand for x = (x - (x * 0.2))
>>> x
8.0

Note that this is really more of an algebra/arithmetic question than a coding question.

var valueInString = "2383";

How do I subtract 35% from number and put it back in the variable?

valueInString = valueInString - 35% 

Something like the above?

Ry-♦

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asked May 22, 2013 at 12:44

If I understand you correctly, you want to subtract 35% of valueInString from valueInString. So it is just some basic math.

var valueInString = "2383";
var num = parseFloat(valueInString);
var val = num - (num * .35);
console.log(val);

Ry-♦

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answered May 22, 2013 at 12:51

epascarelloepascarello

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2

Math:

valueInString = valueInString * (1 - 0.35);

Shorter:

valueInString *= 1 - 0.35;

answered May 22, 2013 at 12:45

Ry-♦Ry-

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3

A nice little utility function for this would be:

const percentageOff = (
  price: number,
  percentageValue: number
): number => {
  return price * (1 - percentageValue / 100)
}

percentageOff(100, 50); // Output: 50

answered Oct 27, 2020 at 13:36

valueInString = valueInString - ((valueInString * 35) / 100);

Ry-♦

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answered May 22, 2013 at 12:48

1

You have two options if you have to subtract percentages as part of a math problem. With the first method, you work out the percentage value and subtract it from the original value. With the second method, you work out the remaining percentage and then calculate the percentage value. Both methods of subtracting percentages are simple, so just choose the one you prefer.

Calculate, Then Subtract

Change the percentage to a decimal. For example, say you have a math problem asking you to work out a sale price of an item. The item's original price was $27.90 and it has 30 percent off in the sale. This means you want to subtract 30 percent from $27.90. Divide the percentage number by 100 to convert to a decimal. In this case, work out

30 ÷ 100 = 0.3

Multiply the original value by the decimal to determine the percentage value. In this example, work out

27.90 × 0.3 = 8.37

Subtract the percentage value from the original price. In this example, work out

27.90 - 8.37 = 19.53

The new price is $19.53.

Subtract, Then Calculate

Take the percentage from 100 to find the remaining percentage. In the previous example, work out

100 - 30 = 70

The remaining percentage is 70 percent.

Divide the remaining percentage number by 100 to convert to a decimal. In this example, work out

70 ÷ 100 = 0.7

Multiply the original value by the remaining percentage decimal. In this example, work out

27.90 × 0.7 = 19.53

The new price is $19.53.

Tips

• If you have a calculator with a percentage (%) key, you can subtract percentages. To subtract 30 percent from $27.90 as per the previous example, type 27.90 − 30 % = to get the answer of 19.53.

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