5 examples on estimation of multiplication and division
Answers
Answer:
Step-by-step explanation:
To estimate the result of multiplication (product), round the numbers to some close numbers that you can easily multiply mentally.
One method of estimation is to round all factors to the biggest digit (place value) they have.
(This is somewhat of a crude method but serves as a starting point in learning estimation.)
For example, estimate 365 × 24. Round 365 to the nearest hundred, and 24 to the nearest ten. So 365 ≈ 400, and 24 ≈ 20. Then 365 × 24 ≈ 400 × 20 = 8000. This way the multiplication is easy to do since it is only a matter of a single digit (4) times a single digit (2), and tagging zeros to the end (000).
Look at other examples:
Estimation
133 × 27
≈ 100 × 30
= 3000
In reality:
2 2
133
× 27
931
2660
3591
Estimation
79 × 73
≈ 80 × 70
= 5600
In reality:
6 2
79
× 73
237
5530
5767
Practice
1. Estimate the products by rounding the factors to the biggest place value.
a. 158 × 32
≈ 200 × 30 = 6000
c. 29 × 94
≈ ____ × ___ = ____
d. 770 × 33
≈ ____ × ___ = ____
f. 88 × 99
≈ ____ × ___ = ____
j. 486 × 21
≈ ____ × ___ = ____
l. 209 × 27
≈ ____ × ___ = ____
2. One purpose of estimation is to catch gross errors in calculations. For example, if you estimate the result to be 5000, and you calculate it to be 354, you know something is wrong since you're way off.
What is best estimate of the options given?
1. 103 × 52
2. 42 × 76
3. 319 × 25
4. 17 × 17
5. 99 × 59
6. 47 × 21
a. 6500
a. 4000
a. 6000
a. 1000
a. 6000
a. 470
b. 500
b. 320
b. 750
b. 200
b. 900
b. 9700
c. 5000
c. 4800
c. 9000
c. 400
c. 9000
c. 1000