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The mean of ten positive numbers is 16. When another number is added, the mean becomes 18. Find the eleventh number.
A. 3
B. 16
C. 38
D. 30
QUICK ANSWER…
C
DETAILS…
If the mean of ten positive numbers is 16, and when another number is added to bring the mean to 18, the eleventh number will be =
Mean = sum of all numbers/ how many numbers being added
Let sum of all the numbers = A
Mean = A/10
A = 10 × mean
A = 10 × 16
A = 160
If another number is added, let the number be = B
New mean = (A + B)/11
18 = (160 + B)/11
18 × 11 = 160 + B
198 = 160 + B
B = 198 – 160
B = 38
Now for the right answer to the above question:
- Option A is incorrect.
- Option B is not correct.
- C is correct.
- D is not the correct answer.
KEY-POINTS…
You may please note these/this:
- Mean = sum of numbers / number of occurrence of numbers
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/ culled from 2021 JAMB-UTME MATHEMATICS question 23 /
