This is a level 2 number link activity from the Figure It Out series. It relates to Stage 5 of the Number Framework.
know how many tens are in whole numbers
use place value knowledge to add tens numbers
This activity does more than ask students to solve problems using tens and hundreds. It also provides an opportunity for them to understand how the base 10 nature of our number system can be used to solve problems that involve numbers that are factors of 10.
The students may solve question 1 by using addition or by using a combination of addition and multiplication. They may see that 10 x 10 is 100 and then add 100 a further nine times to get 1 000. Make sure that they can see the connection between this and working it out as 10 x 10 x 10.
Mira has used a counting-on-in-tens strategy in question 2. Discuss and share other strategies, such as using basic facts and place value ideas to add or subtract. Another strategy may be to use rounding. Mira could have rounded her total up by 30 to get to 100 and then subtracted 10 from that rounding to find that Paora’s 90 was 20 more than her 70.
It’s important to share these strategies and to encourage your students to understand them, but they should not be trying to memorise them. The strategies will be of little value to the students if they become just another learned ritual. Students who are encouraged to look for efficient ways of solving problems are more likely to see the value of adopting some of the shared strategies.
Question 4 has some important connections for students to appreciate. In 4a, the students may see that multiplying or dividing by 100 is a matter of adding or subtracting zeros. Examine this rule with your students and make sure that the idea of multiplying by 100 is seen as more than simply adding two zeros. (Adding zeros to the front of a number makes no difference to a number.) Multiplying by 100 is placing two zeros on the right end because the digits have moved two places to the left. The reverse occurs for division by 100.
In question 4b, you can highlight the connection between multiplying by 1/10 and dividing by 10. The 10 cents can be used as 1/10 of a dollar or as a dollar divided by 10.
Answers to Activity
1. 1 000
2. a. 80 to catch up with James, 140 to catch up with Atareita, and 160 to catch up with Frances
b. 160 more than Mira, 140 more than Paora, 80 more than James, and 20 more than Atareita
4. a. 17 cartons and three extra boxes