Bunuel
If y is the sum of x consecutive positive integers, and x>3, is y odd?
(1) x is odd.
(2) The largest number among the x consecutive integers is odd.
Project DS Butler Data Sufficiency (DS3)
For DS butler Questions Click Here If y is the sum of x consecutive positive integers, and x>3, is y odd?The sum of x consecutive integers equals the mean multiplied by the number of terms, thus x*{mean}=y. Recall that in evenly spaced set mean=median, thus we have that x*{mean}=x*{median}=y.
The question asks whether y is odd.
(1) x is odd --> x*{median}=odd*{median}=y. If a set has odd number of terms the median is the middle term, when arranged in ascending/descending order, thus the median of the set must be an integer. For y to be odd the median must be odd, but the median of odd number of consecutive integers can be odd as well as even, for example, consider {1, 2,
3, 4, 5} and {1, 2, 3,
4, 5, 6, 7}. Not sufficient.
(2) The largest number among the x consecutive integers is odd. If the set is {0,
1, 2, 3}, then y is even but if the set is {1, 2,
3, 4, 5}, then y is odd. Not sufficient.
(1)+(2) The sets we considered to prove insufficiency of the first statement are still valid because both of them have the largest term odd (to satisfy the second statement). Thus even taken together the statements are not sufficient.
Answer: E.