Respuesta :

Answer: 15

Step-by-step explanation:

Let the number that is subtracted = x.

Setting up the equation, we get:

(17-x)/(21-x) = 1/3

We can cross multiply:

3(17-x) = 21-x

Distribute the 3:

51 - 3x = 21 - x

2x = 30

x = 15

Foxzy0

The answer = 15. 17 - 15 = 2. 21 - 15 = 6. 2/6 = 1/3