Question

Chris is 2 years old and Jenny is 4 years old in how many years will Jenny be 7 years younger than twice Chris age

Answer 1

Let's write out all the possibilities. 

2, 3, 4, 5, 6, 7,  8,   9,  10, 11, 12, 13
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15

The correct answer is 7 years.

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Answer 2

C=2 and j=4

j+y=2(c+y)-7

j+y=2c+2y-7  and since j=4 and c=2 we have:

4+y=2*2+2y-7

y+4=2y+4-7

y+4=2y-3

-y+4=-3

-y=-7

y=7

So in 7 years Jenny will be 7 years younger than twice Chris' age.

check...

4+7=2(2+7)-7

11=2(9)-7

11=18-7

11=11