Estimate the sum and difference of the two given numbers by rounding off to nearest 10s and 100s.
Let us round off three numbers 17, 24 and 25 to the nearest 10s.
* We can see that 17 is between 10 and 20 but it is closer to 20 than 10. So, 17 is rounded off to 20.
* 24 is between 20 and 30 but is closer to 20 than 30. So, 24 is rounded off to 20.
* 25 is between 20 and 30. But it is exactly on the middle point. So, 25 is rounded off to 30.
We can easily estimate the sum and difference of any 2 number by rounding off them to nearest values and adding or subtracting them.
1. Estimate the sum by rounding off to the nearest value and find the actual sum.
2. Estimate the difference by rounding off to the nearest value and find the actual difference.
1. Find the sum and difference of the following.
2. Round off the nearest 10.
a.19 ⇒ ~ 20
b. 25 ⇒ ~ 30
c. 21 ⇒ ~ 20
d. 47 ⇒ ~ 50
3. Estimate the sum to the nearest ten and also find the actual sum.
4. Estimate the difference to the nearest ten and also find the actual difference.
Teacher’s note : The teacher should be prepared to give a variety of questions, puzzles, and activities according to the skills of the students.