Ruby Refuses to Divide Correctly

Question

I'm simply trying to get a percentage.

irb(main):001:0> (25 / 50) * 100
=> 0

This should most definitely equal 50, as confirmed by my calculator (copied and pasted the same equation into gcalc). Why does Ruby refuse to do this?

Answer 1

It's doing integer division.

Basically, 25 is an integer (a whole number) and so is 50, so when you divide one by the other, it gives you another integer.

25 / 50 * 100 = 0.5 * 100 = 0 * 100 = 0

The better way to do it is to first multiply, then divide.

25 * 100 / 50 = 2500 / 50 = 50

You can also use floating point arithmetic explicitly by specifying a decimal point as in:

25.0 / 50.0 * 100 = 0.5 * 100 = 50

Answer 2

Because you're dividing an integer by an integer, so the result is getting truncated to integer (0.5 -> 0) before getting multiplied by 100.

But this works:

>> (25 / 50) * 100
=> 0
>> (25.0 / 50) * 100
=> 50.0