Q. A person P asks one of his three friends X as to how much money he had. X replied, “If Y given me Rs. 40, then Y will have half of as much as Z, but if Z gives me Rs. 40, then three of us will have equal amount.” What is the total amount of money that X, Y and Z have ?
Q. Jay and Vijay spent an equal amount of money to buy some pens and special pencils of the same quality from the same store. If Jay bought 3 pens and 5 pencils, and Vijay bought 2 pens and 7 pencils, then which one of the following is correct ?
(a) A pencil costs more than a pen. (b) The price of a pencil is equal to that of a pen (c) The price of a pen is two times the price of a pencil (d) The price of a pen is three times the price of a pencil Correct Answer: (c) The price of a pen is two times the price of a pencil
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Jay and Vijay spent an equal amount of money
Let’s say the price of a pen is x and the price of a pencil is y.
Since Jay and Vijay spent an equal amount of money, we can write an equation to represent this: 3x + 5y = 2x + 7y.
Solving this equation for x and y, we get: 3x + 5y = 2x + 7y 3x – 2x = 7y – 5y ; x = 2y
Q. An amount of money was distributed among A, B and C in the ratio p : q : r.
Consider the following statements : 1. A gets the maximum share if p is greater than (q+r). 2. C gets the minimum share if r is less than (p+q). Which of the above statements is/are correct ? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Correct Answer: (a) 1 only
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Amount of money was distributed among a b and c
Ratio of distribution of money among A, B, and C is p : q : r.
Considering statement 1: If p > (q + r), then p is definitely the largest number. So, A must have got the maximum share. Hence, statement 1 is correct.
Considering statement 2: If r < (p + q), then r may or may not be the smallest number. For example, 5 < (2 + 4) So, C may or may not have got the minimum share. Hence, statement 2 is incorrect.
Q. There are 6 persons arranged in a row. Another person has to shake hands with 3 of them so that he should not shake hands with two consecutive persons. In how many distinct possible combinations can the handshakes take place?
(a) 3 (b) 4 (c) 5 (d) 6 Correct Answer: (b) 4
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
6 Person in a row handshake combinations
Let’s consider the 6 persons in a row as A, B, C, D, E, and F. The person can shake hands with 3 of them in the following distinct combinations:
A C E
A C F
A D F
B D F
In each of these combinations, the person does not shake hands with two consecutive persons. So there are a total of 4 distinct possible combinations for the handshakes to take place, and the correct answer is (b) 4.
Q. Consider the following statements : 1. The sum of 5 consecutive integers can be 100. 2. The product of three consecutive natural numbers can be equal to their sum.
which of the above statements is/are correct? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Correct Answer: (c) Both 1 and 2
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Sum & Product of Consecutive Integers
Problem Part 1 – Five Consecutive Integers Let’s say the first integer is x. The next four numbers are: x+1, x+2, x+3, and x+4 The sum of these five numbers is 5x + 10 If this sum equals 100, then: 5x + 10 = 100 Solving for x: x = 18 Therefore, the five consecutive integers are: 18, 19, 20, 21, 22
Problem Part 2 – Numbers 1, 2, and 3 Sum: 1 + 2 + 3 = 6 Product: 1 × 2 × 3 = 6
Conclusion: Both statements are correct since: 1. We found five consecutive integers that sum to 100 2. For numbers 1, 2, and 3, their sum equals their product
Q. On a chess board, in how many different ways can 6 consecutive squares be chosen on the diagonals along a straight path ?
(a) 4 (b) 6 (c) 8 (d) 12 Correct Answer: (b) 6
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Chess Board Consecutive Squares Chosen
Given: – Chess board has 2 diagonals with 8 squares each – Need to select 6 consecutive squares – These 6 squares must be consecutive along a diagonal
Step 1: Analyze one diagonal – Diagonal has 8 squares – Need to select 6 consecutive squares – Think of 6 squares as one block – This block can slide along diagonal
Step 2: Calculate possible positions on first diagonal – 8 squares total, need 6 consecutive – First position: squares 1-6 – Second position: squares 2-7 – Third position: squares 3-8 Total positions on first diagonal = 3
Step 3: Calculate possible positions on second diagonal – Same calculation as first diagonal – 3 possible positions Total positions on second diagonal = 3
Step 4: Calculate total number of ways – First diagonal: 3 ways – Second diagonal: 3 ways Total ways = 3 + 3 = 6
Q. If the price of an article is decreased by 20% and then the new price is increased by 25%, then what is the net change in the price?
(a) 0% (b) 5% increase (c) 5% decrease (d) Cannot be determined due to insufficient data Correct Answer: (a) 0%
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Price of an article is decreased & increased by 20, 25
Given: – Original price = P – First change: 20% decrease – Second change: 25% increase
Step 1: Calculate price after 20% decrease – Decrease amount = 20% of P = 0.2P – New price = P – 0.2P – New price = 0.8P
Step 2: Calculate final price after 25% increase – Increase amount = 25% of 0.8P = 0.25(0.8P) = 0.2P – Final price = 0.8P + 0.2P – Final price = 1P
Step 3: Calculate net percentage change – Original price = P – Final price = P – Net change = (Final price – Original price)/Original price × 100 – Net change = (P – P)/P × 100 – Net change = 0%