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

1 Answer
Mar 27, 2018

20 pens


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.


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)