What is the first step to estimate the sum of two numbers?
The first step is to round each number to the same place value (like the nearest ten or hundred).
Estimate the sum by rounding each number to the nearest ten: \(47 + 32\)
Round \(47\) to \(50\). Round \(32\) to \(30\). The estimated sum is \(50 + 30 = 80\).
Estimate the sum by rounding each number to the nearest ten: \(88 + 59\)
Round \(88\) to \(90\). Round \(59\) to \(60\). The estimated sum is \(90 + 60 = 150\).
Is an estimated sum the exact answer?
No, it is an approximate answer that is close to the exact sum. The exact sum of \(47 + 32\) is \(79\), while the estimate is \(80\).
Estimate the sum by rounding each number to the nearest hundred: \(214 + 489\)
Round \(214\) to \(200\). Round \(489\) to \(500\). The estimated sum is \(200 + 500 = 700\).
Estimate the sum by rounding each number to the nearest hundred: \(651 + 245\)
Round \(651\) to \(700\). Round \(245\) to \(200\). The estimated sum is \(700 + 200 = 900\).
Sarah has \(52\) red beads and \(39\) blue beads. About how many beads does she have in total?
Round \(52\) to \(50\) and \(39\) to \(40\). Sarah has about \(50 + 40 = 90\) beads.
A school library has \(378\) fiction books and \(235\) non-fiction books. About how many books are there in all?
Round \(378\) to \(400\) and \(235\) to \(200\). There are about \(400 + 200 = 600\) books.
Estimate the sum: \(71 + 15\)
Round \(71\) to \(70\). Round \(15\) to \(20\). The estimated sum is \(70 + 20 = 90\).
Estimate the sum: \(804 + 129\)
Round \(804\) to \(800\). Round \(129\) to \(100\). The estimated sum is \(800 + 100 = 900\).
When you estimate a sum, do you round the numbers first, or add them first?
You must round the numbers FIRST, and then add the rounded numbers.
To estimate \(188 + 54\), is it better to round to the nearest ten or nearest hundred?
Rounding to the nearest ten (\(190 + 50 = 240\)) will give a closer estimate than rounding to the nearest hundred (\(200 + 100 = 300\)). Usually, you round to the largest place value that both numbers have, or as the problem directs.
