Q. There are four letters and four envelopes and exactly one letter is to be put in exactly one envelope with the correct address. If the letters are randomly inserted into the envelopes, then consider the following statements:
1. It is possible that exactly one letter goes into an incorrect envelope. 2. There are only six ways in which only two letters can go into the correct envelopes. Which of the statements given above is/are correct? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Correct Answer: (b) 2 only
Question from UPSC Prelims 2023 CSAT
Explanation :
The first statement is incorrect.
If we have four letters and four envelopes, and we place one letter correctly, then we have three letters and three envelopes left.
If we now place another letter correctly, we would have two letters and two envelopes left, which means either both of these would be correct or both would be incorrect. If we place one of these two letters incorrectly, the last letter would also have to go into the incorrect envelope because there’s only one choice left. Therefore, it’s not possible to have exactly one letter in an incorrect envelope. The possible scenarios are 0, 2, or 4 letters in the correct envelopes.
The second statement is correct.
There are indeed six ways in which only two letters can go into the correct envelopes.
This can be calculated using the combination formula 4C2 (which stands for “”4 choose 2″”), which gives us the number of ways to choose 2 items from a set of 4. The formula is 4! / (2!(4-2)!) = 6. So, the correct answer is (b) 2 only.
Q. AB and CD are 2-digit numbers. Multiplying AB with CD results in a 3-digit number DEF. Adding DEF to another 3-digit number GHI results in 975. Further A, B, C, D, E, F, G, H, I are distinct digits. If E = 0, F = 8, then what is A+B+C equal to ?
(a) 6 (b) 7 (c) 8 (d) 9 Correct Answer: (a) 6
Question from UPSC Prelims 2023 CSAT
Explanation :
Since E = 0 and F = 8, the product of AB and CD must be a number in the form of 08X, where X is a digit from 1 to 9.
The only way to get a product of 08X is if one of the numbers (AB or CD) is a multiple of 4 and the other number ends with 2 or 7.
The possible pairs of numbers are (12, 34), (17, 24), (24, 17), (34, 12).
However, since the sum of DEF and GHI is 975, the sum of the digits D, G, H, I must be 9 (since E = 0 and F = 8).
The only pair of numbers that satisfies this condition is (12, 34), which gives a product of 408.
Q. A flag has to be designed with 4 horizontal stripes using some or all of the colours red, green and yellow. What is the number of different ways in which this can be done so that no two adjacent stripes have the same colour?
Q. Question: Is (p+q-r) greater than (p-q+r), where p, q and r are integers ? Statement-1: (p-q) is positive. Statement-2: (p-r) is negative.
Which one of the following is correct in respect of the above Question and the Statements? (a) The Question can be answered by using one of the Statements alone, but cannot be answered using the other Statement alone. (b) The Question can be answered by using either Statement alone. (c) The Question can be answered by using both the Statements together, but cannot be answered using either Statement alone. (d) The Question cannot be answered even by using both the Statements together. Correct Answer: (c) The Question can be answered by using both the Statements together, but cannot be answered using either Statement alone.
Question from UPSC Prelims 2023 CSAT
Explanation :
From the given question, we need to find whether (p+q-r) is greater than (p-q+r) or not.
Is (p+q-r) greater than (p-q+r), where p, q and r are integers ?
If we simplify this, we get 2q > 2r or q > r. So, we need to determine whether q is greater than r or not.
Statement-1: (p-q) is positive. This means p > q. But this statement doesn’t give any information about r. So, we cannot answer the question using this statement alone.
Statement-2: (p-r) is negative. This means p < r. But this statement doesn’t give any information about q. So, we cannot answer the question using this statement alone.
Using both the statements together, we know that p > q and p < r. This implies that r > p > q or r > q. So, q is not greater than r. Therefore, (p+q-r) is not greater than (p-q+r).
So, the correct answer is (c) The Question can be answered by using both the Statements together, but cannot be answered using either Statement alone.
Q. Question: Is p greater than q? Statement-1: p x q is greater than zero. Statement-2: p^2 is greater than q^2.
Which one of the following is correct in respect of the above Question and the Statements? (a) The Question can be answered by using one of the Statements alone, but cannot be answered using the other Statement alone. (b) The Question can be answered by using either Statement alone. (c) The Question can be answered by using both the Statements together, but cannot be answered using either Statement alone. (d) The Question cannot be answered even. by using both the Statements together. Correct Answer: (d) The Question cannot be answered even. by using both the Statements together.
Question from UPSC Prelims 2023 CSAT
Explanation :
Question – Is p greater than q?
Statement-1: p x q is greater than zero. This statement implies that both p and q are either positive or negative. However, it does not provide information about whether p is greater than q.
Statement-2: p^2 is greater than q^2. This statement implies that the absolute value of p is greater than the absolute value of q. However, it does not provide information about whether p is greater than q, because both p and q could be negative.
Even if we use both statements together, we cannot definitively answer whether p is greater than q. For example, if p and q are both positive and p^2 is greater than q^2, then p is greater than q. But if p and q are both negative and p^2 is greater than q^2, then p is actually less than q.
Therefore, the correct answer is (d) The Question cannot be answered even by using both the Statements together.
The 4-digit numbers less than 2000 formed by the digits 1, 2, 3, and 4 where none of the digits is repeated are 1234, 1243, 1324, 1342, 1423, and 1432.