Question

The ratio of my blue pens to my black pens is `7:2`; I add four more black pens to my collection. How many blue pens must I add to maintain the same ratio of blue to black?

Answer 1

`11:6`

Explanation:

`7:2`

`7-2=5`, so you would have to maintain the difference of `5`. If you added `4` more black pens that would equal to `6` black pens total with `7` blue pens. To maintain the difference of `5` you would need to have `11` blue pens.