Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Rounding to the nearest 10: If the units digit is 5 or more, round up. If it is 4 or less, round down.
Estimation: Finding an approximate answer that is close to the actual value to make calculations easier.
Inverse Operations: Using the opposite operation to check if an answer is correct (e.g., checking addition with subtraction).
Reasonableness: Judging if an answer 'makes sense' based on the estimated value.
📐Formulae
💡Examples
Problem 1:
Estimate the sum of 37 and 52 by rounding to the nearest 10.
Solution:
37 rounds to 40; 52 rounds to 50. 40 + 50 = 90.
Explanation:
Since 7 is greater than 5, 37 rounds up to 40. Since 2 is less than 5, 52 rounds down to 50. The estimated sum is 90.
Problem 2:
Calculate 85 - 23 and use the inverse operation to check your result.
Solution:
85 - 23 = 62. Check: 62 + 23 = 85.
Explanation:
First, perform the subtraction. To check the answer, add the result (62) to the number that was subtracted (23). If you get the starting number (85), the answer is correct.
Problem 3:
Sarah says that 148 + 21 is approximately 200. Is her estimate reasonable?
Solution:
No, the estimate is not reasonable. 150 + 20 = 170.
Explanation:
By rounding 148 to the nearest ten (150) and 21 to the nearest ten (20), the sum is 170. 200 is too far away from the actual numbers to be a helpful estimate.