IPS Maths question

[kandc]

Hello, I'm new to this forum and wondered if anybody could explain how to work out the following question please:

Peter's grandma is 5 times as old as Peter was 3 years ago.
If Peter's grandma is 55, how old is Peter?

The answer in the book says Peter is 13 but I get it to be 14. What would be the best way to work it out? Thank you.

[yoyo123]

I would say it was 14 too

she is 55, which is 5 x 11. so 3 years ago Peter was 11, he is now 14.

depends when his birthday is maybe

[kandc]

That's what I thought - thank you for replying so quickly!

[wiltsman]

Hello, I'm new to this forum and wondered if anybody could explain how to work out the following question please:

Peter's grandma is 5 times as old as Peter was 3 years ago.
If Peter's grandma is 55, how old is Peter?

The answer in the book says Peter is 13 but I get it to be 14. What would be the best way to work it out? Thank you.

Let Peter be p years.

3 years ago Peter was p - 3 years.

Peter's grandma is 5 times as old as this, which is 5(p-3) = 5p - 15

But we also know that grannie is 55, so:

5p - 15 = 55 so
5p = 55 + 15 = 70 so
p = 70/5 = 14