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