Determine if an Estimate is an Overestimate or Underestimate
This Grade 4 Eureka Math skill teaches students to determine whether an estimate is an overestimate or underestimate by analyzing how each number was rounded. In addition, rounding both numbers up produces an overestimate; rounding both down produces an underestimate. In subtraction, rounding the minuend up or the subtrahend down gives an overestimate. For example, estimating 5 and 4/5 + 2 and 7/8 by rounding to 6 + 3 = 9 is an overestimate because both fractions were rounded up. This analytical skill is covered in Chapter 26 of Eureka Math Grade 4.
Key Concepts
To determine if an estimate is an overestimate (greater than the actual answer) or an underestimate (less than the actual answer), analyze how each number was rounded. Addition: If both numbers are rounded up, the sum is an overestimate. If both are rounded down, the sum is an underestimate. Subtraction ($A B$): If $A$ is rounded up and $B$ is rounded down, the difference is an overestimate. If $A$ is rounded down and $B$ is rounded up, the difference is an underestimate.
Common Questions
What is an overestimate?
An overestimate is a rounded answer that is greater than the actual exact answer. This happens when the rounded values used are larger than the originals.
What is an underestimate?
An underestimate is a rounded answer that is less than the actual exact answer. This happens when the rounded values used are smaller than the originals.
How do you know if an estimated sum is an overestimate or underestimate?
If both addends were rounded up, the estimate is an overestimate. If both were rounded down, it is an underestimate. If one went up and one went down, the direction depends on which rounding was larger.
Is rounding 5 and 4/5 to 6 and 2 and 7/8 to 3 an over or underestimate for their sum?
It is an overestimate. Both numbers were rounded up (5 and 4/5 rounded up to 6; 2 and 7/8 rounded up to 3), so the estimated sum of 9 is greater than the actual sum.
How does subtraction affect whether an estimate is over or under?
In subtraction, if the minuend (number being subtracted from) is rounded up or the subtrahend (number being subtracted) is rounded down, the estimate will be an overestimate.