Estimating the Sum of Given Numbers
We need estimation, when we don’t want an exact answer. Estimation is a fare guess of the sum and is close to the actual answer reasonably.
For example; Robin has 37 white marbles and 83 red marbles. About how many marbles Robin has?
To answer the above question we don't need to actually add the given numbers but need to give a good estimation of the sum of the numbers. The best approach to estimating sums is to round to nearest tens, hundreds or thousands.
As the given numbers are less than one hundred we can round them to nearest tens as shown below:
37 rounded to closest tens = 40
83 rounded to closest tens = 80
And 40 + 80 = 120 (we just add tens in our mind i.e. 4 tens + 8 tens = 12 tens = 120)
So, Robin has about 120 marbles all together.
Problem 2: Steve had $785 in his account before he deposited another $518 to his account. Find the approximate balance in Steve's account after the deposit?
Solution: We need to round both the numbers to nearest hundreds in this case and then add the results:
785 rounded to nearest hundreds = 800
518 rounded to nearest hundreds = 500
Estimated sum = 800 + 500 = 1 300
Hence, Steve had approximately $1 300 in his bank account after the deposit.
If 3rd grade students get able to estimate numbers to hundreds, this is a very good basic math achievement in arithmetic. But we can encourage them to do better than that.
Below are the two worksheets to practice and get comfortable with estimating sums for 3rd grade math level;
Below is the link to 2nd grade math page, where you can print all the content for 2nd grade math
2ND GRADE MATH CORE CURRICULUM
Below are the links to my previous posts on 3rd grade math;
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-worksheets-on-estimating-numbers
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-comparing-and-ordering-numbers-1
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-comparing-numbers-worksheets
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-ordering-numbers-worksheets
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-rounding-numbers-to-nearest-ten
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-skip-counting-by-5s-worksheets
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-simple-addition-equations
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-adding-two-4-digit-numbers
https://steemit.com/steemiteducation/@mathworksheets/3rd-grade-math-adding-numbers-when-they-have-different-number-of-digits