Adding and subtracting big numbers

Worked example

2 745 386 + 1 968 457

• Ones: 6 + 7 = 13. Write 3, carry 1 to the tens.
• Tens: 8 + 5 + 1 (carried) = 14. Write 4, carry 1 to the hundreds.
• Hundreds: 3 + 4 + 1 (carried) = 8. Write 8.
• Thousands: 5 + 8 = 13. Write 3, carry 1 to the ten thousands.
• Ten thousands: 4 + 6 + 1 (carried) = 11. Write 1, carry 1 to the hundred thousands.
• Hundred thousands: 7 + 9 + 1 (carried) = 17. Write 7, carry 1 to the millions.
• Millions: 2 + 1 + 1 (carried) = 4. Write 4.

So the cooperative earned 4 713 843 Frw.

Check it: 2 745 386 is about 3 million and 1 968 457 is about 2 million, so the answer should be about 5 million. 4 713 843 is close.

Worked example

A school had 5 000 000 Frw to build a kitchen. It spent 1 468 275 Frw. How much is left?

1. We need 5 000 000 − 1 468 275. The top number is full of zeros, so borrow once from the 5 millions.
2. 5 000 000 is the same as 4 millions + 9 hundred thousands + 9 ten thousands + 9 thousands + 9 hundreds + 9 tens + 10 ones.
3. Now subtract each column from the ones: 10 − 5 = 5, 9 − 7 = 2, 9 − 2 = 7, 9 − 8 = 1, 9 − 6 = 3, 9 − 4 = 5, 4 − 1 = 3.
4. Reading from the left: 3 531 725 Frw is left.

Check it: add the answer to the number you took away. 3 531 725 + 1 468 275 = 5 000 000. ✔

Worked example

A sector had 9 250 000 Frw. It spent 3 785 500 Frw on water tanks and 2 960 750 Frw on school desks. How much money is left?

1. Add what was spent: 3 785 500 + 2 960 750 = 6 746 250 Frw.
2. Subtract from the budget: 9 250 000 − 6 746 250 = 2 503 750 Frw.