|
Problem |
What mental math |
Answer and explanation |
|
16 x 40 |
half and double |
½ of 16 is 8; 2 x 40 is 80; 8 x 80 = 640 |
|
108 x 9 |
distributive property | 108 x 9 = (100 + 8) x 9 = (100 x 9) + (8 x 9) = 900 + 72 = 972 |
| 525 + 83 + 275 | compatible numbers | (525 + 275) + 83 = 800 + 83 = 883 |
|
50 x 29 x 2 |
compatible numbers (and pattern) | (50 x 2) x 29 = 100 x 29 = 2,900 |
|
80 x 900 |
patterns |
8 x 9 = 72 with 3 zeros; 72,000 |
|
2400 ÷ 80 |
patterns |
24 ÷ 8 = 3 with (2-1 = 1) zero; 30 |
|
22 x 50 |
half and double (and pattern) |
½ of 22 is 11; 2 x 50 is 100; 11 x 100 = 1100 |