3rd Grade - Math

LESSON PROBLEM: Computation: You have 10 rice cookies. You give one cookie to each of your 7 friends. How many cookies are left for you?


STUDY GUIDE

You have 9 rice candies. You want to give 1 each to 7 friends. You need 7 candies for your friends. How many rice candies are left for you? Let's see. Draw on a paper nine pieces of candy. Color seven yellow. Color two red.

1 2 3 4 5 6 7 8 9 10

Seven yellow rice candies have been given to your friends. To find out how many you have left, count beyond 7. Count 8 and 9. Two rice candies are left.

Count forward from the number that you want to subtract.


To subtract 8 from 9, count forward from 8. We count one number '9' to find the answer. Draw 9 candies on your paper. Color eight yellow and one red.

1 2 3 4 5 6 7 8 9

You can see that when the yellow candies are subtracted you have one candy left. When subtracting 8 from 9, we get 1. Write it this way: 9 - 8 = 1

Now subtract 5 from 10. Draw ten candies on your paper. Color 5 yellow and 5 red.Count 6, 7, 8, 9 and 10. There are 5 numbers. So, 10 - 5 = 5

1 2 3 4 5 6 7 8 9 10

You can see that your candy is divided into two equal parts. When subtracting 5 from 10, we get 5. Whether we count forward or backward, we count 5 numbers.

Now do the following:

9
-7 8
-5
10
-7
10
-6 7
-2 10
-9 6
-4 5
-4 3
-2 10
-6

How did you do the problems above? Did you use forward or backward counting?

If you picture in your mind the numbers, you will know how far you are from either end. You can then decide whether to count forward or backward. Draw seven rice candies on your paper.

1 2 3 4 5 6 7

You want to subtract 2 from 7. To count forward, count 3, 4, 5, 6, 7. You counted five numbers forward. To count backward, count two numbers back to get the answer. You count 6 and 5.

1 2 3 4 5 6 7
1 2 3 4 5 6
1 2 3 4 5

To get 5, count backwards. Subtract one at a time. When you subtract one, you are left with 6. When you subtract another 1, two in all, you are left with 5. Subtracting is giving away.






ACTIVITIES

Do the following sums using reverse counting and forward counting. Time yourself. See which method is easier and quicker.

9-6, 8-7, 9-6, 8-6, 9-7, 9-8, 8-7, 8-5,

10-8, 10-9, 10-6, 10-7, 10-5, 7-5, 7-5,

8-5, 8-6, 8-7, 8-5, 9-8, 9-7, 9-6, 9-5





EXTENDED LEARNING

If you are given certain problems to solve, which require you to decide whether to use addition or subtraction, how would you go about it?




VOCABULARY

  • recipe
  • difference
  • risotto
  • pilaf
  • forward
  • reverse counting


Click here to play Rice Rampage!
How is Rice Grown:
Farming rice is hard work. Click here to learn more about the Stages of Farming Rice.
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