alleryThe average of 10 numbers is 45. A new number, 100, is added to the set. The new average is:
A45
B50
C55
D72.5
Answer & Solution
Correct answer: B. 50
1. Recover the total first: average x count = 45 x 10 = 450.
2. Adding the new number makes the total 450 + 100 = 550.
3. The count is now 11.
4. So the new average is 550 / 11 = 50.
5. 72.5 comes from averaging 45 and 100 directly, which ignores that one number cannot outweigh ten.
_Source: syllabus Maths, Ch 13 'Statistics', S13.2 Mean of Grouped Data_
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