This is an algebra problem where you need to get rid of one variable so that you can solve for the other variable. Start by translating each sentence into an equation. We have 2 pieces of information
(1) "Right now Bob is 2.5 times as old as Al." So, Bob = 2.5 x Al.
Let's let B stand for Bob and A stand for Al. So: B=2.5A
(2) In 5 years, Bob will be only twice as old as Al. S: Bob+5years = 2 (Al + 5 years).
Let's show that as:
B+5=2 (A +5). And multiply out to give:
(2a) B+5=2A+10
Now, here is the trick - take the first piece of information (B=2.5A) and substitute it into equation (2a) so that there is new equation with only one variable - A.
(3) 2.5A + 5=2A+10.
And then solve algebraically:
2.5A=2A +10 -5
2.5A = 2A +5
2.5A - 2A= 5
.5A = 5
A = 10
Now check the answer:
B= 2.5 x 10. So, Bob is 25 if Al is 10
In 5 years, Bob will be 30 and Al will be 15. 30 =2x15. Therefore B=2A.
I hope this helps.
