Estimation (Intro) — Answer Key
Part A: Sort the Words
Sort each word or number into the correct category box.
1. Round each number to the nearest 10, then sort it by whether that rounded ten is under 50 or 50 and above.
Rounded ten is under 50
23 rounds to 2031 rounds to 3012 rounds to 10 Rounded ten is 50 or above
47 rounds to 5068 rounds to 7055 rounds to 60 Grouping rounded tens as under 50 or 50+ is the first step toward rounding to the nearest 100, a Grade 2 preview skill.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. When you round 23 to the nearest 10 you get 20.
Numbers 20-24 round down to 20 because 0-4 rounds down.
2. 47 rounded to the nearest 10 is 50.
7 is 5 or more so 47 rounds up to 50 on the number line.
3. The rounded ten 20 is less than 50.
20 is smaller than 50, so it fits the 'under 50' group.
4. The rounded ten 70 is greater than 50.
70 is larger than 50 so it belongs in the '50 or above' group.
5. 55 rounds up to the nearest ten of 60.
The rule says 5 rounds up, so 55 becomes 60 which is above 50.
Part C: True or False?
Read each statement. Circle True or False.
1. 31 rounds to 30 and 30 is under 50.
True False
31 has a 1 in the ones place, rounds to 30, and 30 is less than 50.
2. 68 rounds to 70 and 70 is under 50.
True False
70 is bigger than 50, so it belongs in the '50 and above' group, not under 50.
3. 12 rounds to 10 and 10 is under 50.
True False
10 is less than 50, so 12 after rounding belongs to the 'under 50' group.
4. All numbers that round to 50 or more are small numbers.
True False
Numbers rounding to 50 or more are the larger half in our two-group sort, not the smaller half.