The third grade students would like to send letters to their pen pals, but not all of them have the right stamps to do so. Can you help them figure out which stamps they need to match the costs of the letters? If any of them have insufficient stamps, put a big ‘X’ across the envelope to let them know that they can’t send the letter with those stamps. This fun addition worksheet gets students to use their critical thinking skills as they try adding various numbers to see if they can get the desired sum.