Step-by-step explanation:
For multiplying 2 digit numbers, I like to multiply the ones place and the tens place separately, then add the result.
For example:
45 × 61
45 × 60 + 45 × 1
For the first product, we can repeat the process:
40 × 60 + 5 × 60 + 45 × 1
2400 + 300 + 45
2745
To check our answer, we can round 45 up to 50, and 61 down to 60.
50 × 60 = 3000
This is close to our answer of 2745, so that makes sense.
Let's try another:
83 × 27
83 × 20 + 83 × 7
80 × 20 + 3 × 20 + 80 × 7 + 3 × 7
1600 + 60 + 560 + 21
2241
Using rounded numbers:
80 × 30 = 2400
Let's do one more:
63 × 87
63 × 80 + 63 × 7
60 × 80 + 3 × 80 + 60 × 7 + 3 × 7
4800 + 240 + 420 + 21
5481
Using rounded numbers:
60 × 90 = 5400
