Question

Mark bought a notebook for $1.45 and some pencils. The pencils cost $0.42 each. The total cost of the notebook and pencils was $6.91. How many pencils did Mark buy?

a.12
b.13 c.14
d.15

Answer 1

Let the number of pencils he bought be x.

cost of notebooks + cost of pencils = cost of notebooks and pencils
Remember that he only bought "a" notebook.

Now think about this:
If I have bought an unknown number of candies for $2 and each candy was $1, how many candies did I buy?
The answer is 2.

Same goes with the pencils. If you buy x pencils for 0.42 each, then the total cost he spent on the PENCILS is 0.42x.

Plug it back to the equation 1 above, and you should get the answer.