Question

Fifteen children voted for their favorite color. The votes for red and blue together were double the votes for green and yellow together. How did the children vote?

Answer 1

We know that there are 15 children altogether 

We know that the number that voted for B+R is double the number of students voted for G+Y

B+R = 2(G+Y)

Think of two numbers that add up to 15, one number is twice of the other number. 

For example, 6 and 12.
12 is double of 6 but 6 + 12 doesn't give 15

So, think again

for example 5 and 10
10 is double of 5 and 5+10 does give 15

So, the number that voted Red and Blue is 10 and the number that voted Yellow and Green is 5