Evie wants groups of three notebooks and five pens. she already has 12 notebooks. how many pens will she need?

To put it in simple term, Evie wants 5 pens for every 3 notebooks.  For us to find out how many pens she will need, you simply need to group the 12 notebooks she has into 3.  So you divide 12 by 3 which gives us 4 groups of 3 notebooks.  But she needs 5 pens for every 3 notebooks.  So you simply multiply the 4 groups of notebooks into 5.  That's 4 groups of notebooks for every 5 pens.  That will give us 20, yes 20 pens. Now for us to be sure that we are getting it correctly.  Let's do it in reverse.  There are 20 pens with 12 notebooks.  Their common multiplier is 4.  Divide 20 by 4 to get 5 pens. Divide 12 by 4 and that will give us 3 notebooks. Therefore we got our answers right.