Prelims Solution

S1: There are not more than two figures on any page of a 51-page book.  S2: There is at least one figure on every page. 

Q. Two statements S1 and S2 are given below followed by a Question:

S1: There are not more than two figures on any page of a 51-page book.
S2: There is at least one figure on every page.

Question: Are there more than 100 figures in that book?
Which one of the following is correct in respect of the above Statements and the Question?
(a) Both S1 and S2 are sufficient to answer the Question, but neither S1 alone nor S2 alone is sufficient to answer the Question.
(b) S1 alone is sufficient to answer the Question.
(c) S1 and S2 together are not sufficient to answer the Question.
(d) S2 alone is sufficient to answer the Question.
Correct Answer: (c) S1 and S2 together are not sufficient to answer the Question.

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

PROBLEM: Can we determine if there are more than 100 figures in the book?

GIVEN:
Statement S1: Not more than 2 figures on any page; 51 pages
Statement S2: At least 1 figure on every page

ANALYSIS:
1. Maximum figures possible:
– 2 figures/page × 51 pages = 102 figures

2. Minimum figures possible:
– 1 figure/page × 51 pages = 51 figures

3. Range of possible total figures:
51 to 102 figures

CONCLUSION: Cannot determine if there are more than 100 figures
REASON: The actual number could be anywhere between 51 and 102 figures

ANSWER: Given information is insufficient to answer the question

S1: There are not more than two figures on any page of a 51-page book.  S2: There is at least one figure on every page.  Read More »

Q. Consider the following arrangement that has some missing letters:

Q. Consider the following arrangement that has some missing letters:

abab_b_bcb_dcdcded_d
The missing letters which complete the arrangement are
(a) a, b, c, d
(b) a, b, d, e
(c) a, c, c, e
(d) b, c, d, e
Correct Answer: (c) a, c, c, e

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

The pattern is a b a b a / b c b c b / c d c d c /d e d e d

Q. Consider the following arrangement that has some missing letters: Read More »

Q. A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel?

Q. A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel?

(a) 10 kg
(b) 15 kg
(c) 20 kg
(d) 25 kg
Correct Answer: (a) 10 kg

Question from UPSC Prelims 2020 CSAT Paper

Explanation :

A vessel full of water weighs 40 kg

GIVEN:
– Full vessel weighs 40 kg
– One-third filled vessel weighs 20 kg

SOLUTION:
1. Weight difference = 40 – 20 = 20 kg
This is weight of 2/3 water

2. Weight of 1/3 water = 20/2 = 10 kg

3. Empty vessel weight = Weight of 1/3 filled – Weight of 1/3 water
= 20 – 10 = 10 kg

ANSWER: The empty vessel weighs 10 kg

Q. A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel? Read More »

Q. A man takes half time in rowing a certain distance downstream than upstream. What is the ratio or the speed in still water to the speed of current? 

Q. A man takes half time in rowing a certain distance downstream than upstream. What is the ratio or the speed in still water to the speed of current?

(a) 1:2
(b) 2:1
(c) 1:3
(d) 3:1
Correct Answer: (d) 3:1

Question from UPSC Prelims 2020 CSAT Paper

Explanation :

PROBLEM: Find ratio of man’s speed in still water to current speed

FORMULAS:
Time = Distance/Speed
– Downstream time = Distance/(v + c)
– Upstream time = Distance/(v – c)

SOLUTION:
1. Speeds:
– Downstream = v + c
– Upstream = v – c

2. Since downstream time is half:
v + c = 2(v – c)
v + c = 2v – 2c
-v + 3c = 0
v = 3c

3. Therefore:
Man’s speed : Current speed
= v : c
= 3 : 1

ANSWER: The ratio of man’s speed in still water to current speed is 3:1

Q. A man takes half time in rowing a certain distance downstream than upstream. What is the ratio or the speed in still water to the speed of current?  Read More »

1. The minimum number of points of intersection of a square and a circle is 2. 2. The maximum number of points of intersection of a square and a circle is 8.

Q. Consider the following statements:

1. The minimum number of points of intersection of a square and a circle is 2.
2. The maximum number of points of intersection of a square and a circle is 8.

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: (b) 2 only

Question from UPSC Prelims 2020 CSAT Paper

Explanation :

Minimum number & maximum of points of intersection of a square and circle

Statement 1 is incorrect. The minimum number of points of intersection between a square and a circle can be 0 if the circle is entirely inside or outside the square.

Statement 2 is correct. The maximum number of points of intersection between a square and a circle is 8. This can happen when the circle passes through all four corners of the square and intersects each side once.

So only statement 2 is correct. Therefore, the correct answer is indeed (b) 2 only.

1. The minimum number of points of intersection of a square and a circle is 2. 2. The maximum number of points of intersection of a square and a circle is 8. Read More »

Q. A digit n > 3 is divisible by 3 but not divisible by 6. Which one of the following is divisible by 4?

Q. A digit n > 3 is divisible by 3 but not divisible by 6. Which one of the following is divisible by 4?

(a) 2n
(b) 3n
(c) 2n + 4
(d) 3n+ 1
Correct Answer: (d) 3n+ 1

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

Digit n > 3 is divisible by 3

Since n is divisible by 3 but not divisible by 6, it means that n must be an odd multiple of 3. Let’s take n=9 as an example.

(a) 2n = 2 * 9 = 18 which is not divisible by 4

(b) 3n = 3 * 9 = 27 which is not divisible by 4

(c) 2n +4 = (2 *9) +4 =22 which is not divisible by 4

(d) 3n +1 = (3 *9)+1=28 which is divisible by 4

So the correct answer is (d) 3n+1.

Q. A digit n > 3 is divisible by 3 but not divisible by 6. Which one of the following is divisible by 4? Read More »

Q. A bottle contains 20 litres of liquid A.

Q. A bottle contains 20 litres of liquid A.

4 litres of liquid A is taken out of it d replaced by same quantity of liquid B. Again 4 litre of the mixture is taken out and replaced by same quantity of liquid B. What is the ratio of quantity of liquid A to that of liquid B in the final mixture?

(a) 4:1
(b) 5:1
(c) 16:9
(d) 17: 8
Correct Answer: (c) 16:9

Question from UPSC Prelims 2020 CSAT Paper

Explanation :

PROBLEM: Find the final ratio of liquids A and B after two replacements

STEP 1: After First Replacement
– Liquid A = 16 litres
– Liquid B = 4 litres
– Total = 20 litres
– Ratio of A to total = 16/20 = 4/5

STEP 2: Second Replacement
– 4 litres mixture removed
– Liquid A removed = 4 × 4/5 = 3.2 litres
– Liquid A remaining = 16 – 3.2 = 12.8 litres
– Liquid B = 20 – 12.8 = 7.2 litres

STEP 3: Final Ratio
12.8:7.2 simplifies to 16:9

ANSWER: The final ratio of liquid A to liquid B is 16:9

Q. A bottle contains 20 litres of liquid A. Read More »

Q. In adult population or a city, 40% men and 30% women are married.

Q. In adult population or a city, 40% men and 30% women are married.

What is the percentage of married adult population if no man marries more than one woman and no woman marries more than one man; and there are no widows and widowers?

(a) 232/7%
(b) 34%
(c) 240/7%
(d) 35%
Correct Answer: (c) 240/7%

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

PROBLEM: Find percentage of married adults in population

GIVEN:
– 40% men are married
– 30% women are married
– Each marriage has one man and one woman

SOLUTION:
Let M = number of men
W = number of women

1. Since married men = married women:
0.4M = 0.3W
W = (4/3)M

2. Total Population N = M + W = M + (4/3)M = (7/3)M

3. Total married adults = 0.4M + 0.3W
= 0.4M + 0.3(4/3)M
= 0.8M

4. Percentage = (0.8M)/(7/3)M = (0.8 × 3)/7 = 2.4/7
= 240/7%
≈ 34.29%

ANSWER: 240/7% or approximately 34.29%

Q. In adult population or a city, 40% men and 30% women are married. Read More »

Q. What is the missing @ term in the following?

Q. What is the missing @ term in the following?

ACPQ : BESU:: MNGI: @

(a) NPJL
(b) NOJM
(c) NPIL
(d) NPJM
Correct Answer: (d) NPJM

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

acpq: besu:: mngi: @

PATTERN: ACPQ → BESU
Letter Shifts:
– 1st letter: +1
– 2nd letter: +2
– 3rd letter: +3
– 4th letter: +4

Starting Word: MNGI
Applying shifts:
M + 1 = N
N + 2 = P
G + 3 = J
I + 4 = M

ANSWER: NPJM

Q. What is the missing @ term in the following? Read More »

Q. The letters from A to Z are numbered from 1 to 26 respectively. If GHI = 1578 and DEF = 912, then what is ABC equal to?

Q. The letters from A to Z are numbered from 1 to 26 respectively. If GHI = 1578 and DEF = 912, then what is ABC equal to?

(a) 492
(b) 468
(c) 262
(d) 246
Correct Answer: (d) 246

Question from UPSC Prelims 2020 CSAT Paper

Explanation : 

ghi=1578 def=912 abc= ?

ALPHABETS TO NUMBERS:
ABC = 123
DEF = 456
GHI = 789

DOUBLING THE NUMBERS:
ABC: 123 × 2 = 246
DEF: 456 × 2 = 912
GHI: 789 × 2 = 1578

Pattern: Each three-letter group when doubled gives the result shown on the right side.

Q. The letters from A to Z are numbered from 1 to 26 respectively. If GHI = 1578 and DEF = 912, then what is ABC equal to? Read More »