Mathematical Operations on Whole Numbers up to 100,000
Primary 4 · Mathematics
Mathematical Operations on Whole Numbers up to 100,000
Lesson 4 of 5
30 min
Let's begin
A bus company in Musanze sold 24 685 tickets in January and 18 947 tickets in February. The manager wants to know the total for both months. The numbers are too big to count on your fingers, but the column method makes it easy.
Write the numbers one under the other, with ones under ones, tens under tens, and so on. Add from the right. When a column makes 10 or more, write the ones digit and carry the ten to the next column.
| TTh | Th | H | T | O | |
| carry | 1 | 1 | 1 | 1 | |
| 2 | 4 | 6 | 8 | 5 | |
| + | 1 | 8 | 9 | 4 | 7 |
| 4 | 3 | 6 | 3 | 2 |
The company sold 43 632 tickets.
The school needs 50 000 Frw for a new football net and has saved 27 368 Frw. How much more does it need? Work out 50 000 − 27 368.
We cannot take 8 ones from 0 ones, and the tens, hundreds and thousands are 0 too. So we borrow (regroup) from the 5 ten-thousands: 50 000 is the same as 4 ten-thousands, 9 thousands, 9 hundreds, 9 tens and 10 ones.
| TTh | Th | H | T | O | |
| regrouped | 4 | 9 | 9 | 9 | 10 |
| − | 2 | 7 | 3 | 6 | 8 |
| 2 | 2 | 6 | 3 | 2 |
The school still needs 22 632 Frw.
Check it by adding: 22 632 + 27 368 = 50 000. The answer is right!
Tip
Line up, then start on the right. Ones under ones, always. And check every subtraction by adding your answer back: you should get the number you started with.
Work each one in your exercise book first. Then tap Show answer to check.
36 458 + 27 391
Answer: 63 849
70 205 − 38 467
Answer: 31 738
A farmer harvested 12 750 kg of maize and sold 8 965 kg. How much maize is left?
Answer: 3 785 kg (12 750 − 8 965)
During umuganda, a sector planted 23 480 trees in one month and 19 675 trees the next month. How many trees altogether?
Answer: 43 155 trees
What number goes in the box? ☐ + 25 000 = 61 340
Answer: 36 340, because 61 340 − 25 000 = 36 340
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
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