MI3 wrote:Q. What is the minimum percentage increase in the mean of set X {-4, -1, 0, 6, 9} if its two smallest elements are replaced with two different primes?
(A) 25% (B) 50% (C) 75% (D) 100% (E) 200%
IMO answer is E, am I correct?
Average = Sum/Number.
Since the number of elements is not changing, the increase in the average will come solely from the increase in the sum.
Thus, to determine the percent increase in the average, we just need to compare the smaller sum to the larger sum.
Old sum = -4 + -1 + 0 + 6 + 9 = 10.
The two smallest primes are 2 and 3.
Replacing -4 and -1 with 2 and 3, we get:
New sum = 2+3+0+6+9 = 20.
20 is 100% greater than 10:
Difference/Original * 100 = (20-10)/10 * 100 = 100%.
The correct answer is
D.
Answer choice E is a trap.
Although 20 is 200%
of 10 -- answer choice E -- it is only 100%
greater than 10.
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