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IPS Maths question
Posted: Sun Sep 06, 2009 12:02 pm
by 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.
Posted: Sun Sep 06, 2009 12:06 pm
by 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
Posted: Sun Sep 06, 2009 12:10 pm
by kandc
That's what I thought - thank you for replying so quickly!
Re: IPS Maths question
Posted: Sun Sep 06, 2009 12:24 pm
by wiltsman
kandc wrote: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