154951

15 5 x 7 9 17

7 + 9 + 17 = (33 + x)/4 = mean

15 + 5 = (20 + x)/3 = mean

(20 + x)/3 = (33 + x)/4

Solve to find x.

1. Take away the division.

4(20 + x) = 3(33 + x)

2. Expand the bracket

80 + 4x = 99 + 3x

3. Take away 3x from both sides.

80 + 4x= 99 + 3x
-3x -3x

80 + x = 99

4. Take away 80 from both sides.

80 + x = 99
-80 -80

x = 19

5. Make sure to check it.

7 + 9 + 17 + 19 = 52/4 =13
15 + 5 + 19 = 39/3 = 13

13 is the mean.