Samacheer Kalvi Class 4 Maths Solutions Term 3 Chapter 2 Numbers Exercise 2.4

Estimate the Following Numbers to Nearest Tens and Then Add or Subtract.

Question 1. Estimate 45 and 93 to the nearest tens and then add them.
Answer: To estimate 45 to the nearest ten, we look at the ones digit. Since the ones digit (5) is at or above 5, we round up, making 45 become 50. For 93, the ones digit (3) is below 5, so we round down, making 93 become 90. Now, we add these rounded numbers: 50 + 90 = 140. This estimation helps us quickly find an approximate sum.
In simple words: First, we round 45 up to 50 and 93 down to 90. Then, we add 50 and 90 together to get 140.

🎯 Exam Tip: When rounding to the nearest ten, always check the ones digit: if it's 5 or more, round up; if it's less than 5, round down.

Question 2. Estimate 42 and 38 to the nearest tens and then add them.
Answer: To estimate 42 to the nearest ten, we check the ones digit (2). Since 2 is less than 5, we round down, making 42 become 40. For 38, the ones digit (8) is 5 or more, so we round up, making 38 become 40. Adding these rounded numbers, 40 plus 40, results in 80. This gives us a quick idea of the total. Rounding makes calculations simpler.
In simple words: We round 42 down to 40 and 38 up to 40. Then, we add 40 and 40, which makes 80.

🎯 Exam Tip: Rounding numbers before adding or subtracting helps to quickly get an approximate answer, especially for large numbers.

Question 3. Estimate 78 and 32 to the nearest tens and then subtract.
Answer: To estimate 78 to the nearest ten, we look at the ones digit (8). Since 8 is 5 or more, we round up, making 78 become 80. For 32, the ones digit (2) is less than 5, so we round down, making 32 become 30. Subtracting these rounded numbers, 80 minus 30, leaves us with 50. This gives a fast, estimated difference. Estimation is useful for quick checks.
In simple words: First, we round 78 up to 80 and 32 down to 30. Then, we take 30 away from 80, which leaves 50.

🎯 Exam Tip: When doing estimation, always make sure to round each number correctly before performing the operation (addition or subtraction).

Question 4. Estimate 91 and 75 to the nearest tens and then subtract.
Answer: To estimate 91 to the nearest ten, we observe the ones digit (1). Since 1 is less than 5, we round down, making 91 become 90. For 75, the ones digit (5) is 5 or more, so we round up, making 75 become 80. Subtracting the rounded numbers, 90 minus 80, gives us 10. This is a quick way to find an approximate answer. The exact answer (16) is close to our estimate.
In simple words: We round 91 down to 90. We round 75 up to 80. Then, we subtract 80 from 90, which results in 10.

🎯 Exam Tip: When a number ends in 5, always remember the rule to round up to the next higher ten.