Question

Evie wants groups of 3 notebooks and 5 pens. She already has 12 notebooks. How many pens will she need?

Answer 1

20 pens

Explanation:

She has four times the amount of notebooks as 1 group would have (1 group=3 notebooks, 5 pens). That means she also needs four times the amount of pens.

`5*4=20`

Another way to solve this would be to set up a proportion.

`3/5=12/p rarr` Number of notebooks over number of pens, `p` represents the number of pens. The ratio of notebooks to pens (or the other way around) stays the same no matter how many groups there are (there are still 5 pens for every 3 notebooks).

`3p=60 rarr` Cross multiply (12 multiplied by 5, p multiplied by 3)

`p=20`