Problem solving math

Question

Judy bought some pens. 5/12th were black. If she bought 60 black pens how many pens did she buy all together?

Answer 1

60 pens are black. 5/12 of her total number of pens are black.

 

So 60 must be 5/12 of all of her pens. We have the sentence

60 is 5/12 of all her pens.

Let all her pens be p (or, say she has p pens). So

60 is 5/12 of p.

"Of" means multiply, and "is" means equal. So we get

60=5/12•p

 

Now we have an equation. Let's multiply both sides by 12 to get

720=5p

Divide both sides by 5 to get

144=p.

 

So Judy bought 144 pens.