Question

A piano has white keys and black keys in the ratio of 13 : 9. If there are 52 white keys,how many black keys are there?

Answer 1

✡ Answer: 9/36 ✡

- - Why?

Because if you look at it like this:

$\frac{13}{52} = \frac{9}{36}$

- 52 being the white and 36 because the black.

✡Hope this helps✡

Answer 2

Let w = white and b = black.
Using the proportion,
13/w = 9/b
Since w = 52 white keys, therefore
13/52 = 9/b
b = 36 black keys