We learn the basics of estimating a sum. Here we learn an easy way to estimate a sum of two numbers by rounding them up.

In the case of two-digit numbers, we can only round the number to the nearest ten, that is, only estimate one place.

For example, we estimate the following sums:

(i) 47 + 32

We need to round the number up to the nearest 10.

47 → 50

32 → 30

50 + 30 = 80

(ii) 25 + 34

We need to round the number up to the nearest 10.

25 → 30

34 → 30

30 + 30 = 60

(iii) 75 + 13

We need to round the number up to the nearest 10.

75 → 80

13 → 10

80 + 10 = 90

1. Estimate the sums of 72 and 48

Solution:

We round the number to the nearest 10.

72 → 70

48 → 50

So 72 is the closest to 70 and 48 is the closest to 50

70 + 50 = 120

So the estimated sum = 120

2. Estimate the sums to the nearest ten and also find the actual sum of 87 and 79.

Solution:

We round the number to the nearest 10.

87 → 90

79 → 80

So 87 is closest to 90 and 79 is closest to 80

90 + 80 = 170

So the estimated total = 170

The actual sum of 87 and 79

87 + 79 = 166

So the actual total is 166

Note:To estimate to the next 10, we see the digit / number in its own place. It will be converted to 0 or 10 accordingly. If the digit / number < 10/2 ist, wird sie in Null umgewandelt, und wenn sie > Is 10/2, it is converted to 10.

In the case of three-digit numbers, we can only round the number to the nearest ten, that is, only estimate one place.

For example, we estimate the following sums:

1. Estimate the sums of 586 and 120

Solution:

We’ll round the number to the nearest hundred.

586 → 600

120 → 100

So, 586 is a hundred closest is 600 and 120 is a hundred closest to 100

600 + 100 = 700

So the estimated sum to the next hundred= 700

We round the number to the nearest ten.

586 → 590

120 → 120

So, 586 is ten nearest is 590 and 120 is nearest hundred is 120

590 + 120 = 710

So the estimated sum over the next ten= 710

2. Round up the numbers 389 and 535 to the nearest 100. Find the estimated and actual total.

Solution:

Round off the numbers to the nearest 100 So 400 + 500 = 900 is the estimated total.

Questions and answers about estimating a sum:

I. Round the numbers shown to the nearest 100s. Find the estimated and actual total.

 Estimated sum Actual amount (i) 582 and 157 __________ __________ (ii) 245 and 163 __________ __________ (iii) 812 and 111 __________ __________ (iv) 345 and 198 __________ __________

Reply:

(i) 800, 739

(ii) 400, 408

(iii) 900, 923

(iv) 500, 543

3rd grade math class

From estimating a sum to HOE PAGE

Did you not find what you were looking for? Or would you like to know more aboutMath only math.
Use that google search to find what you need.