Math Focus 4
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## CHAPTER 3: ADDITION AND SUBTRACTION

### Lesson 9: Subtracting by Renaming

Use these interactive activities to encourage students to have fun on the Web while learning about addition and subtraction. Students can try these activities on their own or in pairs.

Goal

Use renaming to make subtraction easier.

Builds Upon

Student Book pages 92–93

Instructions for Use

Subtraction to 100 (3 min) , Subtraction to 100 (2 min), Subtraction to 100 (90 s), Subtraction to 100 (1 min)andSubtraction to 100 (30 s) allow students to subtract numbers up to 3 digits while playing against a 3 min, 2 min, 90 s, 1 min, and 30 s clock, respectively.

To use any site, read its instructions. Ensure that the “Num Lock” key on your keyboard is on and click in the coloured problem area to start the timer. Subtract the numbers mentally from right to left, using renaming when possible. Then type in your answer, starting with the hundreds digit first, by using the number keys at the right of your keyboard. Backspace over any mistyped numbers and correct them, and then press “Enter” on your keyboard. A score sheet at the lower left of the problem area shows your time remaining in seconds and the number of problems you have answered correctly and incorrectly. See how many problems you can get correct in the time available, and then click on the yellow bar below to start a new round.

Subtraction of Four Digit Numbers lets students practice subtracting 4-digit numbers.

To use Subtracting Four Digit Numbers, read the directions, scroll down to “Practice”, and click on “Start”. A pair of numbers will display at the left of the equals sign as a timer counts elapsed time in the “Report Totals” box below. Enter your answer in the box right of the equals sign and click on “check”. Use renaming when you can. If correct, a new pair of numbers will be displayed. If not, an error box will display the correct answer. Click “OK” to resume play. You can vary the game by scrolling down to “Play” and clicking on one of the 3 yellow boxes on the left.

QUIA Math Journey lets students practice adding and subtracting 3- and 4-digit numbers.

To use QUIA Math Journey, read the directions, click “3-digit numbers” and “4-digit numbers” under
“Addition” or “Subtraction”, and click on “Begin the Game”. A problem will be displayed for you to solve. Your objective is to fly around the world, city by city, by solving problems like this. Although the problems must be answered exactly, estimate to check that each answer that you input into the empty answer box is reasonable before clicking on “Check Answer”. If an answer is right, you will score air distance travelled and receive a new problem. If it is wrong, you will miss your flight and be shown the correct answer. Click on “Continue” to get a new problem.  If you miss three flights, the game ends. To play a new game at any time, click on “Start over”.