Basic Mathematics

Estimating

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Estimating
Estimating is a way of getting an approximate answer to a problem by making the calculations simpler. One method of estimating is by rounding.

There are different rules for estimating by rounding:

1. Estimating sums or differences

2. Estimating products

3. Estimating quotients
Estimating
To estimate a sum (or a difference), round all addends to the highest place value of the smallest addend. Then add these rounded addends.
Estimate 287 + 53 + 7,258
The smallest addend is 53. The highest place value in 53 is the tens place.
Round all the addends to the tens place and then add.
Estimating
Click on the best estimate of the sum.
299 + 372
    7
500
700
600
800
Question 1 of 8
Round 299 to 300 and 372 to 400. Then add the rounded numbers. Try again.
Round 299 to 300 and 372 to 400. Then add the rounded numbers. Try again.
300 + 400 = 700
Round 299 to 300 and 372 to 400. Then add the rounded numbers. Try again.
Round 299 to 300 and 372 to 400. Then add the rounded numbers. Try again.
Round the addends to the nearest hundred. Then add the rounded numbers.
Estimating
Click on the best estimate of the sum.
89 + 793 + 608
1,800
2,300
1,490
2,000
1,100
Question 2 of 8
Round 89 to 90, 793 to 790, and 608 to 610. Then add the rounded numbers. Try again.
Round 89 to 90, 793 to 790, and 608 to 610. Then add the rounded numbers. Try again.
90 + 790 + 610 = 1,490
You may have rounded the addends to the nearest thousands. Round each addend to the nearest ten. Try again.
Round 89 to 90, 793 to 790, and 608 to 610. Then add the rounded numbers. Try again.
Round the addends to the nearest ten. Then add the rounded numbers.
Estimating
Click on the best estimate of the difference.
711 - 196
900
800
400
500
600
Question 3 of 8
You may have rounded correctly and then added. Subtract the rounded numbers instead of adding. Try again.
Round 711 to 700 and 196 to 200. Then subtract. Try again.
Round 711 to 700 and 196 to 200. Then subtract. Try again.
700 - 200 = 500
Round 711 to 700 and 196 to 200. Then subtract. Try again.
Round both numbers to the nearest hundred. Then subtract the rounded numbers.
Estimating
Click on the best estimate of the difference.
4,726 − 591
4,300
5,200
5,300
4,100
4,200
Question 4 of 8
Round 4726 to 4700 and 591 to 600. Then subtract. Try again.
Round 4726 to 4700 and 591 to 600. Then subtract. Try again.
You may have rounded correctly and then added. Subtract the rounded numbers instead of adding. Try again.
4,700 - 600 = 4,100
Round 4726 to 4700 and 591 to 600. Then subtract. Try again.
Round both numbers to the nearest hundred. Then subtract the rounded numbers.
Estimating
To estimate a Product, round each factor to its highest place value. Then multiply these rounded factors.
Estimate 287 × 53.
First, round 287 to 300 and round 53 to 50. Then find the product:
The estimated product is 15,000.
Estimating
To estimate a quotient, round the divisor to its highest place value. Divide to find the first digit of the quotient. Then add zeros to complete the estimated quotient.
Estimate 19,328 ÷ 625.
First, round the divisor 625 to 600.
Divide to find just the first digit of the estimated quotient.
600 divides into 1932 about 3 times.
Add zero as needed to complete the place value.
The estimated quotient is 30.
Estimating
Click on the best estimate of the product.
38 × 51
19,500
     195
20,000
  2,000
     200
Question 5 of 8
Round 38 to 40 and 51 to 50. Then multiply. Try again.
Round 38 to 40 and 51 to 50. Then multiply. Try again.
Round 38 to 40 and 51 to 50. Think about how many zeros are in the product. Try again.
40 × 50 = 2,000
Round 38 to 40 and 51 to 50. Think about how many zeros are in the product. Try again.
Round both factors to the nearest ten. Then multiply the rounded numbers.
Estimating
Click on the best estimate of the product.
12 × 998
15,000
13,900
  1,000
10,000
  1,200
Question 6 of 8
Round 12 to 10 and 998 to 1000. Then multiply. Try again.
Round 12 to 10 and 998 to 1000. Then multiply. Try again.
Round 12 to 10 and 998 to 1000. Think about how many zeros are needed in the product. Try again.
10 × 1000 = 10,000
Round 12 to 10 and 998 to 1000. Think about how many zeros are in the product. Try again.
Round both factors to their highest place value. Then multiply the rounded numbers.
Estimating
Click on the best estimate of the quotient.
4,812 ÷ 207
  20
    2
  30
200
  28
Question 7 of 8
4812 ÷ 200 is about 20.
The first digit of the quotient is 2. Don't forget the zeros needed to fill out the place value. Try again.
Round 207 to 200. Then estimate the first digit of the quotient, and add zeros as needed. Try again.
The first digit of the quotient is 2, but two zeros are not needed to fill out the place value. Try again.
Round 207 to 200. Then estimate the first digit of the quotient, and add zeros as needed. Try again.
Round the divisor to the nearest hundred. Then estimate the first digit of the quotient.
Estimating
Click on the best estimate of the quotient.
18,875 ÷ 62
3,000
     30
   300
3,100
       3
Question 8 of 8
The first digit of the quotient is 3, but three zeros are not needed to fill out the place value. Try again.
The first digit of the quotient is 3. More than one zero is needed to fill out the place value. Try again.
18,875 ÷ 60 is about 300.
Round 62 to 60. Then estimate the first digit of the quotient, and add zeros to compute the quotient. Try again.
The first digit of the quotient is 3. Don't forget the zeros needed to fill out the place value. Try again.
Round the divisor to the nearest ten. Then estimate the first digit of the quotient.
Estimating