Provide students a multiplication, addition or subtraction problem and ask them to estimate the answer. Explain to them that estimation means "about." When students estimate, they are figuring out the approximate value of the answer. Let your third-grade students know that as they start to work with larger numbers in addition, subtraction and multiplication, estimation will help them.
Round each number in the problem to its nearest whole number in tens. Round down numbers that end in one to four and round up numbers that end in five to nine. For example, 54 rounds down to 50 and 17 rounds up to 20. Numbers less than 10 should not be rounded.
Tell students to complete the problem in their heads, using the rounded numbers, e.g., 50 + 20 = 70, which is the estimated value of 54 + 17. The estimated value of 54 - 17 is 30 and of 54 * 17 is 1,000.
Perform the calculations with the original numbers so students can check the accuracy of their estimates. For 54 + 17 the actual value is 71; for 54 - 17, it is 37; and for 54 * 17, it is 918.
Explain to students that when working with two-digit numbers, the estimated result will be within 10 for addition and subtraction, and within 100 for multiplication.