2010 General Studies, all questions
UPSC Prelims 2010 · General Studies
Question 40: Basic Numeracy
A person X has four notes of Rupee 1, 2, 5 and 10 denomination. The number of different sums of money she can form from them is
a16
b15
c12
d8
AnswerThe answer is (b).
With one note each of Rs 1, 2, 5 and 10, every different selection of notes gives a sum. There are 2^4 - 1 = 15 non-empty selections, and no two give the same total (1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 15, 16, 17, 18), so 15 different sums can be formed. Remember: for n distinct notes check for repeated totals before counting 2^n - 1.
Why each option is right or wrong
- (a) 16 counts the empty selection, which is not a sum of money.
- (b) Right: 15 non-empty selections, all with different totals.
- (c) 12 undercounts the possible sums.
- (d) 8 undercounts the possible sums.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2010, General Studies, Series A. The paper on upsc.gov.in.