Respuesta :

devishri1977

Answer:

25 black keys

Step-by-step explanation:

Let the number of requires black keys = 'x'

White key : Black keys = 7 : 5

7 : 5  :: 35 : x

Product of extremes = product of means

             7 *x = 35 * 5

                  x = [tex]\frac{35*5}{7}[/tex]

                 x = 5 *5

                 x = 25