Practice!

Sample Problem

Gary has half as many stamps as Frank. Rex has 38 more stamps than Gary. The average number of stamps each of them has is 214. How many stamps does Frank have?

  stamps

Solution

Since each boy has an average of 214 stamps, they have 214 × 3 = 642 stamps altogether.

Since Gary has half as many stamps as Frank, Frank’s stamps = Gary’s stamps × 2.

Since Rex has 38 more stamps than Gary, Rex’s stamps = Gary’s stamps + 38.

We can solve this problem using trial and error. Pick a number for Gary’s stamps, plug in for Frank’s stamps and Rex’s stamps, and add the three numbers together to see if the sum equals 642. If your first number doesn’t work, pick a smaller number if the sum is too big and a bigger number if the sum is too small. Keep doing this until you get 642 as your sum.

 

Number of

Gary’s Stamps

Number of

Frank’s stamps

Number of

Rex’s stamps

Sum

100

100 × 2 = 200

100 + 38 = 138

100 + 200 + 138 = 438

150

150 × 2 = 300

150 + 38 = 188

150 + 300 + 188 = 638

155

155 × 2 = 310

155 + 38 = 193

155 + 310 + 193 = 658

152

152 × 2 = 304

152 + 38 = 190

152 + 304 + 190 = 646

151

151 × 2 = 302

151 + 38 = 189

151 + 302 + 189 = 642

 

Frank has 302 stamps.