Question:
The mean of 21 numbers is 9. One of the numbers, 19, is deleted. What is the mean of the remaining 20 numbers?
The mean of 21 numbers is 9. One of the numbers, 19, is deleted. What is the mean of the remaining 20 numbers?
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When one observation is deleted, subtract its value from the total sum and divide by the new count.
Updated On: Jul 13, 2026
- 6.4
- 8.5
- 18.889
- 21.25
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The mean is the sum of observations divided by the number of observations.
Step 2: Key Formula or Approach:
Total sum = Mean \(\times\) Number of observations.
Step 3: Detailed Explanation:
Total sum of 21 numbers = \(9 \times 21 = 189\).
After deleting 19, the sum of the remaining 20 numbers = \(189 - 19 = 170\).
New mean = \(\frac{170}{20} = 8.5\).
Thus, the mean of the remaining 20 numbers is 8.5.
This matches option (B).
The answer is straightforward.
The mean is the sum of observations divided by the number of observations.
Step 2: Key Formula or Approach:
Total sum = Mean \(\times\) Number of observations.
Step 3: Detailed Explanation:
Total sum of 21 numbers = \(9 \times 21 = 189\).
After deleting 19, the sum of the remaining 20 numbers = \(189 - 19 = 170\).
New mean = \(\frac{170}{20} = 8.5\).
Thus, the mean of the remaining 20 numbers is 8.5.
This matches option (B).
The answer is straightforward.
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