Question

Fill in the blank to make an equivalent ratio X : 3 = 40 : 15

Answer 1

So look at the patterns. 
How much bigger is 15 to 3? 
Answer = 5x bigger.
What is 5x smaller than 40? (in other words, 5 x ? = 40)
Answer = 8!

So, the missing 'x' = 8