wunder beta🎯 Estimating and Checking Answers
Round numbers to the nearest 10 or 100 to predict an answer before you calculate, then use the opposite operation to prove your answer is right.
What you’ll learn
- Estimate, Then CheckEstimate sums and differences by rounding to the nearest 10 or 100, and check answers with inverse operations.Estimating means rounding numbers to the nearest ten or hundred and adding the round numbers to predict an answer: 48 + 31 is about 50 + 30 = 80. After calculating the exact answer, check it with the opposite operation — 79 − 31 = 48 proves 48 + 31 = 79. Estimating catches wild errors; checking makes answers certain.
Questions this course answers
Rounded to the nearest ten, what is 48?
48 is closer to 50 than to 40, so it rounds to 50.
Estimate 48 + 31 by rounding to the nearest ten.
48 rounds to 50 and 31 rounds to 30, so the estimate is 50 + 30 = 80.
About how much is 312 + 189, rounded to the nearest hundred?
312 rounds to 300 and 189 rounds to 200, so about 300 + 200 = 500.
How can you check that 48 + 31 = 79?
Subtraction undoes addition: 79 − 31 = 48 confirms the sum.
Why estimate BEFORE you calculate?
An estimate sets your expectation, so a badly wrong answer is easy to spot.
Grounded in trusted sources
- Khan Academy Kids
- PBS Kids — early math
- NAEYC — early math learning
- Britannica Kids
Every Wunder lesson is built from real, reputable sources — never invented.
Related Math courses
Wunder is a personalized learn-anything platform — tell it any topic and it builds a beautiful, fact-checked course in minutes, with narration, a knowledge check, and a college-style University track.
Browse more Math courses · All topics · Home
© 2026 Wunder Learning LLC · Terms & Privacy