Year 4
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We can estimate and check the result of a calculation.
We can round numbers to the nearest 10 and 100
Year 4 Unit 9
What we are learning:
- When rounding to the nearest 10, the rounded value will always be a multiple of 10. (10, 20, 30, 40 ….)
- When rounding to the nearest 10, if the units value is 0, 1,2,3, or 4 round DOWN to the nearest 10. If the units value is 5,6,7,8 or 9 round UP to the nearest 10.
- When rounding to the nearest 100, the rounded value will always be a multiple of 100. (100, 200, 300 …)
- When rounding to the nearest 100, if the tens value is 0,10,20,30 or 40 round DOWN to the nearest 100. If the tens value is 50, 60, 70 80 or 90 round UP to the nearest 100.
- An estimate is a sensible guess of the actual value, usually with some thought or calculation involved.
- Estimating should be very quick. Children who are given too much time to make an estimate question why they should not just calculate the actual value.
- Subtraction is the inverse of addition, (undoes addition), and addition is the inverse of subtraction.
ACTIVITY 1: ESTIMATING AND CHECKING
ACTIVITY 2: ESTIMATING FOR ADDITION
ACTIVITY 3: ESTIMATING FOR FINDING THE DIFFERENCE
Activities you can do at home:
From the sheet “Estimating” choose two numbers from block A. Estimate the total of these two numbers:
round both numbers (up or down) to the nearest 10 and add to calculate their total.
From the sheet “Estimating” choose two numbers from block B. Estimate the total of these two numbers:
round both numbers (up or down) to the nearest 100 and add together to calculate their total.
From the sheet “Estimating” choose one number from block B and one from block C. Estimate the difference between these two numbers: round both numbers (up or down) to the nearest 100 and subtract the lower value from the higher value.
Using an appropriate written method of calculation. Calculate the total of 27+45. Use the inverse operation (the inverse of addition is subtraction) to check the answer by subtracting either 27 or 45 from the total.
27 + 45 = 72
72 – 27 = 45
72 – 45 = 27
Good questions to ask and discuss:
Why do we round numbers to the nearest 10 or 100?
How can it help us making estimates?
How can estimates help us in calculations?
Is estimating the same as guessing?
If your child:
Is not sure whether to round up or down
Draw a number line together to establish that when rounding to 10, the number 5 is exactly half way. When this happens, or if the digit in the units column is more than 5 we round UP. If it is 4 or less we round DOWN. If it is a zero we are already on a ten, so we don’t have to round at all.
The same principle applies to rounding to 100, where 50 or more rounds up.
Extension Activity
Please use this activity when you think your child understands the unit of work. It will deepen and extend your child’s understanding of this unit.