Question

Sally is 3 years older than Jill was 5 years ago. Write an algebraic expression for both of their ages. If Jill is 10, how old is Sally?

Answer 1

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.