A2D2
Bunuel
GMAT Club Official Explanatio:
If the data set S = {2, 3, 4, ..., 17}, how many subsets of S have a sum of 142?A. 2
B. 3
C. 4
D. 5
E. 6
Firstly, let's calculate the sum of the original set: 2 + 3 + 4 + ... + 17 = (2 + 17)/2 * 16 = 152.
We need to find the number of subsets with a sum of 142, which is 10 less than the sum of S.
Essentially, we need to count the subsets that total 10, because excluding them from S results in a subset summing to 142.
- The one-element subset summing to 10 is {10};
- Two-element subsets summing to 10 are {2, 8}, {3, 7}, and {4, 6}.
- The only three-element subset summing to 10 is {2, 3, 5}.
We cannot have a four-element subset summing to 10 because the smallest sum of any four elements in S is 2 + 3 + 4 + 5 = 14.
Therefore, there are five subsets summing to 142,
those remaining if we remove {10}, {2, 8}, {3, 7}, {4, 6}, and {2, 3, 5}, from {2, 3, 4, ..., 17}.
Answer: D.
We have found how many subsets need to be not counted, I.e, 5, how is that and of how many subset will make the sum upto 142?
We don’t know the total combinations
Removing {10} from S:
Subset: {2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17}
Removing {2, 8} from S:
Subset: {3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17}
Removing {3, 7} from S:
Subset: {2, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17}
Removing {4, 6} from S:
Subset: {2, 3, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17}
Removing {2, 3, 5} from S:
Subset: {4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17}
Each of these subsets sums to 142.