Ms. Smith bought 30 boxes of pencils in the beginning of the year. Each box cost $2.15 including tax. 6/15 of the boxes she bought have been used. How much money did she spend on the remaining boxes?

$45

Step-by-step explanation:

In order to begin solving this problem, we need to first calculate the number of remaining (unused) boxes. We do this by multiplying the total number of boxes by the percentage of boxes remaining. Since Mr. Smith used 6/15 of the boxes we know that there are 9/15 remaining (15-6 = 9). If we divide 9 by 15 we get 0.60 which is the percentage of remaining boxes in decimal form. Now we simply multiply this by the total initial number of boxes

30 * 0.60 = 18 remaining boxes

Now that we know how many unused boxes there are, we simply multiply this number by the cost of each box.

18 * $2.15 = $45