Question

find the missing number: 20/30= square root of 20/?
A.9
B.30
C.45
D.900

Answer 1

20/30= square root of 20/?
2/3 = 2√5/x
2x = 6√5
x = 3√5 or √45

check:
√20 / √45
= √(20/45)
= √(4/9) = 2/3 or 20/30

Answer 2

or, assuming the usual carelessness with parentheses,
2/3 = √(20/x)
4/9 = 20/x
4x = 180
x = 45
check: 2/3 = √(20/45) = √(4/9) yep.