Estimation Strategies

Show your work for each problem.

1.
What is rounded to the nearest ten?
1. a)100
2. b)110
3. c)90
4. d)95
Answer: 100
and . So . The exact answer is 99, which is very close to our estimate!
2.
Round to the nearest ten.
Answer: 80
78 has 8 in the ones place. Since , we round up to 80.
3.
Which is the best estimate for ?
1. a)500
2. b)550
3. c)600
4. d)700
Answer: 600
and . So . The exact answer is 601.
4.
Use front-end estimation: What is approximately?
Answer: 700
Front-end estimation: . The exact answer is 799, so this is a reasonable estimate.
5.
Estimate using rounding.
Answer: 60
1. Round 83 to the nearest ten 80
2. Round 27 to the nearest ten 30
3. Subtract: 80 - 30 = ? 60
6.
Use compatible numbers to estimate .
1. a)38
2. b)45
3. c)35
4. d)40
Answer: 40
160 is close to 156 and divides evenly by 4. . The exact answer is 39.
7.
Estimate by rounding 23 to the nearest ten.
Answer: 80
. So . The exact answer is 92.
8.
You have 30 euros. Items cost 7 euros, 9 euros, and 11 euros. Can you buy all three?
Answer: yes
1. Round 7 euros to the nearest 5 5
2. Round 9 euros to the nearest 5 10
3. Round 11 euros to the nearest 5 10
4. Add: 5 + 10 + 10 = ? 25
5. Is 25 less than 30? (yes/no) yes
9.
A calculator shows . Using estimation, is this reasonable?
1. a)Cannot determine
2. b)No, it's too high
3. c)No, it's too low
4. d)Yes, it's reasonable
Answer: No, it's too high
. The calculator shows 24960, which is about 10 times too high! The correct answer is 2496.
10.
Use compatible numbers: Estimate .
Answer: 50
. The exact answer is 49, so 50 is an excellent estimate!
11.
Use front-end estimation with adjustment for .
Answer: 820
1. What is the front-end estimate? (500 + 200) 700
2. Look at remaining digits: 87 + 34. Estimate this sum. 120
3. Add front-end and adjustment: 700 + 120 = ? 820
12.
Which is the best strategy to estimate ?
1. a)Rounding (190 ÷ 6)
2. b)No estimation needed
3. c)Compatible numbers (180 ÷ 6 = 30)
4. d)Front-end (100 ÷ 6)
Answer: Compatible numbers (180 ÷ 6 = 30)
Compatible numbers: is easy to calculate mentally. The exact answer is 31.5, so 30 is a good estimate!
13.
Estimate by rounding.
Answer: 2000
. So . The exact answer is 1990.
14.
Your car travels 28 miles per gallon. Gas costs 4 dollars per gallon. Estimate the gas cost for a 350-mile trip.
Answer: 50
1. Use compatible numbers: 350 ÷ 28 ≈ 360 ÷ 30 = ? 12
2. That's about 12 gallons. At 4 dollars per gallon: 12 × 4 = ? 48
3. Round to a nice number for your estimate 50
15.
Why might you want to overestimate when budgeting money?
1. a)To get an exact answer
2. b)To make math easier
3. c)To avoid running out of money
4. d)Overestimating is always wrong
Answer: To avoid running out of money
When budgeting, overestimating is safer. If you think items cost more than they do, you'll have extra money left over instead of coming up short!
16.
Round to the nearest ten.
Answer: 30
34 has 4 in the ones place. Since , we round down to 30.
17.
Estimate by rounding each number to the nearest ten.
Answer: 150
1. Round 67 to the nearest ten 70
2. Round 45 to the nearest ten 50
3. Round 28 to the nearest ten 30
4. Add: 70 + 50 + 30 = ? 150
18.
Use compatible numbers to estimate .
Answer: 80
. The exact answer is 77.875, so 80 is a good estimate!