It means finding an answer that is 'close' to the real answer. You usually do this by rounding the numbers first before adding.
Estimate the sum of \(398 + 504\) by rounding each number to the nearest hundred.
\(398\) rounds to \(400\). \(504\) rounds to \(500\). The estimated sum is \(400 + 500 = 900\).
Why is estimating a useful skill in addition?
It helps you check if your final, exact answer is reasonable. If your answer is very far from your estimate, you might have made a mistake.
A library has \(245\) fantasy books and \(379\) science fiction books. ABOUT how many books is that in total?
To estimate, you can round. \(245\) is about \(250\). \(379\) is about \(380\). So, \(250 + 380 = 630\). Or, round to hundreds: \(200 + 400 = 600\). The library has about \(600\)-\(630\) books.
What are some 'key words' that often tell you to add in a word problem?
Words like: total, sum, all together, in all, plus, combined, increase by.
Maria scored \(482\) points in a video game. On the next level, she scored another \(535\) points. What is her total score?
The key word is 'total'. You need to add. \(482 + 535 = 1,017\) points.
Estimate the sum of \(121 + 288\) by rounding to the nearest ten.
\(121\) rounds to \(120\). \(288\) rounds to \(290\). The estimated sum is \(120 + 290 = 410\).
A farmer planted \(1,250\) corn seeds and \(875\) bean seeds. How many seeds did he plant in all?
The key phrase is 'in all'. You need to add. \(1,250 + 875 = 2,125\) seeds.
Now find the exact sum of \(398 + 504\).
\(398 + 504 = 902\). This is very close to our earlier estimate of \(900\), so the answer is likely correct.
The school cafeteria sold \(176\) slices of pizza on Monday and \(215\) slices on Tuesday. How many slices were sold all together?
The key words are 'all together'. You need to add. \(176 + 215 = 391\) slices.
Your estimate for a problem is \(500\), but your exact answer is \(945\). What does this likely mean?
It likely means you made a mistake in your addition, because the exact answer is not close to the estimate. You should re-check your work.
There are \(440\) students in the elementary school and \(582\) students in the middle school. How many students are there in total?
