Nines, place value puzzles and three-digit sums
Answers are for parents and teachers.
1
Use the finger trick or 10 × n − n to find 9 × 9 and 9 × 4.
9 × 9 = 90 − 9 = 81 and 9 × 4 = 40 − 4 = 36.
2
The tens digit of a nines product is 5. Which multiplication fact is it?
9 × 6 = 54. The tens digit 5 is 1 less than 6, and 5 + 4 = 9.
3
Write 5,086 in expanded form.
5,000 + 80 + 6.
4
A shop sold 349 kg of rice on Monday and 476 kg on Tuesday. How many kilograms is that in all?
300 + 400 = 700, 40 + 70 = 110 and 9 + 6 = 15. 700 + 110 + 15 = 825 kg.
5
Marina adds 568 + 237 by place value, as the table shows, and says the answer is 705. Is she right? Find the sum.
| Place | Add | Result |
|---|---|---|
| Hundreds | 500 + 200 | 700 |
| Tens | 60 + 30 | 90 |
| Ones | 8 + 7 | 15 |
No. 700 + 90 + 15 = 805. Marina forgot that 15 ones need regrouping, so the sum is 805.