A strang math calculation

Question

Consider the following calculation

3 * 20.9

normally it equals to 62.7. However, when I calculate it in javascript, the output is 62.699999999999996. And what's more I found that 7, 11 will also produce the wrong answer. Why it goes wrong and how to make it right? I think it's about the binary?

demo

It's because of the floating point precision. http://stackoverflow.com/questions/1458633/how-to-deal-with-floating-point-number-precision-in-javascript — Steve Buzonas, May 27 '15 at 07:36
Duplicate question: [Is floating point math broken?](http://stackoverflow.com/questions/588004/is-floating-point-math-broken) — Yogi, May 27 '15 at 07:36
The imprecision occurs because 0.9 can't be mapped to a finite binary floating point number. You can use libraries such as BigDecimal if this poses a problem for you: https://github.com/dtrebbien/BigDecimal.js/ — Alex, May 27 '15 at 07:37

score 0 · Accepted Answer · answered May 27 '15 at 07:38

0

To keep only 1 decimal. Use

(3*20.9).toFixed(1)

Updated Fiddle

answered May 27 '15 at 07:38

Zee

8,420
5
36
58

score 0 · Answer 2 · answered May 27 '15 at 07:39

0

Try this:

Number((3*20.9).toFixed(1));

answered May 27 '15 at 07:39

Radonirina Maminiaina

6,958
4
33
60

A strang math calculation

2 Answers2