Answer: 13 (and Sally will always be 3 years older than Jill)
Step-by-step explanation:
Let S and J stand for Sally and Jill's ages. We are told:
- (S-5) = (J-5)+3 [Sally is 3 years older than Jill was 5 years ago] The 5 years ago is the reason for the (S-5) and (J-5) expressions.
If Jill is 10, how old is Sally?
(S-5) = (J-5)+3
(S-5) = (10-5)+3
S-5 = 8
S = 13
We actually don't really need an equation for solving this, other than the question asks us to write one. It doesn't matter how many years later, since Sally is 3 years older, she will always remain 3 years older, if we ignore the likelihood that the statement doesn't hold true for the period between their actual birthdays.
