Mark bought a notebook for $1.45 and some pencils for $0.42 each. if the total cost was $6.91, how many pencils did he buy?
a.12
b.13
c.14
d.15

B - 13

Okay, we know that Mark brought 1 notebook and the totally is 6.91 while one pencil costs $0.42.

x= number of pencils he brought.
we know the price of 1 notebook + the cost of pencils times the numbers of pencils he brought = total cost.

So the equation will be:

1.45 + 0.42x = 6.91  subtract 1.45 on both sides.
0.42x = 5.46   Then we solve for x by dividing both sides by 0.42
x= 13

So the number of pencils he brought is 13.