This activity is designed to provide students with practice adding single-, two-, and three-digit whole numbers. Students should try to do the calculations mentally or on paper. Calculators may be used to check calculations.
Some students will need help to interpret the problems, particularly with vocabulary such as “total”, “two-digit”, and “double”. Encourage students to identify the relevant information in each task. For example, the important information in question 2 is “two aliens” and “the numbers … add up to 157”.
Other contextual information needs to be discarded.
Help students develop estimation strategies involving sensible rounding by discussing the different methods they have used. For example, you could ask students to estimate the answer to question 1b: 210 + 332 + 95 + 62. By rounding, the problem solution might be estimated by 210 + 330 + 100 + 60 = 700.

Answers to Activity

1. a. 492 b. 289 c. 1459
d. 29 e. 349 f. 2762
2. 95 and 62
3. 212 + 210 = 422
4. Answers will vary.
5. 3140
6. The aliens not working would add up to 870. One option would be aliens with the numbers 652, 212, and 6 on their tummies.