Prelims Solution

Q. Joseph visits the club on every 5th day, Harsh visits on every 24th day, while Sumit visits on every 9th day. If all three of them met at the club on a Sunday, then on which day will all three of them meet again ?

Q. Joseph visits the club on every 5th day, Harsh visits on every 24th day, while Sumit visits on every 9th day. If all three of them met at the club on a Sunday, then on which day will all three of them meet again ?

(a) Monday
(b) Wednesday
(c) Thursday
(d) Sunday
Correct Answer: (b) Wednesday

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

Joseph visits the club on every 5th day

– Joseph visits every 5th day
– Harsh visits every 24th day
– Sumit visits every 9th day
– They first meet on a Sunday

Solution Method:
1. Find LCM of visit intervals (5, 24, 9)
– LCM = 360 days

2. Calculate odd days
– 360 ÷ 7 = 51 weeks + 3 days
– Extra days after complete weeks = 3

3. Count days from Sunday
– Starting day: Sunday
– Add 3 days
– Final day: Wednesday

Answer: (b) Wednesday

Q. Joseph visits the club on every 5th day, Harsh visits on every 24th day, while Sumit visits on every 9th day. If all three of them met at the club on a Sunday, then on which day will all three of them meet again ? Read More »

Statement: Some radios are mobiles. All mobiles are computers. Some computers are watches.

Statement: Some radios are mobiles. All mobiles are computers. Some computers are watches.

Conclusion-I: Certainly some radios are watches.
Conclusion-II: Certainly some mobiles are watches.
Which one of the following is correct?

(a) Only Conclusion-I
(b) Only Conclusion-II
(c) Both Conclusion-I and Conclusion-II
(d) Neither Conclusion-I nor Conclusion-II
Correct Answer: (d) Neither Conclusion-I nor Conclusion-II

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

Relations between radios, mobiles, computers, and watches

Given statements:
1. Some radios are mobiles
2. All mobiles are computers
3. Some computers are watches

Analysis of conclusions:

Conclusion I: “Some radios are watches”
– We can only say some radios are computers
– We can’t establish a definite connection between radios and watches
– Not valid

Conclusion II: “Some mobiles are watches”
– All mobiles are computers
– But only some computers are watches
– No definite connection between mobiles and watches
– Not valid

Answer: (d) Neither Conclusion-I nor Conclusion-II follows

Relations between radios mobiles computers and watches

Statement: Some radios are mobiles. All mobiles are computers. Some computers are watches. Read More »

Q. In a class, 60% of students are from India and 50% of the students are girls. If 30% of the Indian students are girls, then what percentage of foreign students are boys?

Q. In a class, 60% of students are from India and 50% of the students are girls. If 30% of the Indian students are girls, then what percentage of foreign students are boys?

(a) 45%
(b) 40%
(c) 30%
(d) 20%
Correct Answer: (d) 20%

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

In a class 60 of students are from india

Given:
– Total students = 100
– Indian students = 60%
– Foreign students = 40
– Total girls = 50%
– Indian girls = 30% of 60 = 18

Step-by-step solution:
1. Foreign girls = Total girls – Indian girls
= 50 – 18 = 32

2. Foreign boys = Total foreign – Foreign girls
= 40 – 32 = 8

3. Percentage of boys among foreign students
= (8/40) × 100 = 20%

Answer: (d) 20%

class 60 of students

Q. In a class, 60% of students are from India and 50% of the students are girls. If 30% of the Indian students are girls, then what percentage of foreign students are boys? Read More »

Q. A woman runs 12 km towards her North, then 6 km towards her South and then 8 km towards her East. In which direction is she from her starting point?

Q. A woman runs 12 km towards her North, then 6 km towards her South and then 8 km towards her East. In which direction is she from her starting point?

(a) An angle less than 45o South of East
(b) An angle less than 45o North of East
(c) An angle more than 45o South of East
(d) An angle more than 45o North of East
Correct Answer: (b) An angle less than 45o North of East

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

A woman runs 12km

Initial position: (0,0)
Movements:
1. North 12 km → (0,12)
2. South 6 km → (0,6)
3. East 8 km → (8,6)

Final position: (8,6)

Direction calculation of women:

– Angle = tan⁻¹(6/8)
– Angle = tan⁻¹(0.75)
– Angle = 36.87°

Since:
– tan 45° = 1
– 6/8 = 0.75 < 1
– Therefore, angle is less than 45°

woman runs 12 km

Q. A woman runs 12 km towards her North, then 6 km towards her South and then 8 km towards her East. In which direction is she from her starting point? Read More »

Q. A bank employee drives 10 km towards South from her house and turns to her left and drives another 20 km.

Q. A bank employee drives 10 km towards South from her house and turns to her left and drives another 20 km.

She again turns left and drives 40 km, then she turns to her right and drives for another 5 km. She again turns to her right and drives another 30 km to reach her bank where she works. What is the shortest distance between her bank and her house?

(a) 20 km
(b) 25 km
(c) 30 km
(d) 35 km
Correct Answer: (b) 25 km

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

A bank employee drives 10 km south

Starting point: (0,0) – House

Movement sequence:
1. South 10 km → (0, -10)
2. Left turn, East 20 km → (20, -10)
3. Left turn, North 40 km → (20, 30)
4. Right turn, East 5 km → (25, 30)
5. Right turn, South 30 km → (25, 0) – Bank

Shortest distance calculation:
– Using Pythagorean theorem
– Distance = √[(x₂-x₁)² + (y₂-y₁)²]
– Distance = √[(25-0)² + (0-0)²]
– Distance = √(625 + 0)
– Distance = √625
– Distance = 25 km

Therefore, the shortest distance between her house and bank is 25 kilometers.

A bank employee drives 10 km

Q. A bank employee drives 10 km towards South from her house and turns to her left and drives another 20 km. Read More »

Q. Images of consonants of the English alphabet (Capitals) are observed in a mirror. What is the number of images of these which do not look like their original shapes?

Q. Images of consonants of the English alphabet (Capitals) are observed in a mirror. What is the number of images of these which do not look like their original shapes?

(a) 13
(b) 14
(c) 15
(d) 16
Correct Answer: (b) 14

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

Mirror images of consonants of the english alphabet

To determine the number of consonant letters in the English alphabet whose mirror images do not resemble their original shapes, follow these steps:

1. Identify the Consonants:

The English alphabet consists of 26 letters. The vowels are A, E, I, O, and U. Sometimes Y is considered a vowel, but typically it’s treated as a consonant in such contexts.
Consonants: B, C, D, F, G, H, J, K, L, M, N, P, Q, R, S, T, V, W, X, Y, Z
Total Consonants: 21

2. Determine Symmetrical Letters:

A letter is considered symmetrical if its mirror image is identical to the original. For capital letters, the following consonants are symmetrical:

– Symmetrical Consonants: H, M, T, V, W, X, Y
Total Symmetrical Consonants: 7

3. Calculate Non-Symmetrical Consonants:

Subtract the number of symmetrical consonants from the total number of consonants to find the number of non-symmetrical consonants.

Non-Symmetrical Consonants: 21 (total) – 7 (symmetrical) = 14
Answer: (b) 14

Q. Images of consonants of the English alphabet (Capitals) are observed in a mirror. What is the number of images of these which do not look like their original shapes? Read More »

Statement: Some cats are almirahs. Some almirahs are chairs. All chairs are tables.

Statement: Some cats are almirahs. Some almirahs are chairs. All chairs are tables.

Conclusion-I: Certainly some almirahs are tables.
Conclusion-II: Some cats may not be chairs.

Which one of the following is correct?
(a) Only Conclusion-I
(b) Only Conclusion-II
(c) Both Conclusion-I and Conclusion-II
(d) Neither Conclusion-I nor Conclusion-II
Correct Answer: (c) Both Conclusion-I and Conclusion-II

Question from UPSC Prelims 2021 CSAT Paper

Explanation :

Some cats are almirahs

Conclusions from Cat, Almirah, Chair Statement

Given Statements:
1. Some cats are almirahs
2. Some almirahs are chairs
3. All chairs are tables

Let’s analyze each conclusion:

Conclusion I: “Some almirahs are tables”

– Some almirahs are chairs (given)
– All chairs are tables (given)
– Therefore, those almirahs that are chairs must also be tables
– This makes Conclusion I logically valid

Conclusion II: “Some cats may not be chairs”

– Some cats are almirahs (given)
– Some almirahs are chairs (given)
– We don’t know if ALL cats are almirahs
– We don’t know if ALL almirahs are chairs
– Therefore, it’s possible that some cats may not be chairs
– This makes Conclusion II logically valid

Answer: Both conclusions I and II logically follow from the given statements.

Statement: Some cats are almirahs. Some almirahs are chairs. All chairs are tables. Read More »

Q. A person X from a place A and another person Y from a place B set out at the same time to walk towards each other.

Q. A person X from a place A and another person Y from a place B set out at the same time to walk towards each other.

The places are separated by a distance of 15 km. X walks with a uniform speed of 1.5 km/hr and Y walks with a uniform speed of 1 km/hr in the first hour, with a uniform speed of 1.25 km/hr in the second hour and with a uniform speed of 1.5 km/hr in the third hour and so on.

Which of the following is/are correct?
1. They take 5 hours to meet.
2. They meet midway between A and B.
Select the correct answer using the code given below:
(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 : 

A person X from place a & other Y from B

Given information:
– Total distance between A and B = 15 km
– Person X’s speed = constant 1.5 km/hr
– Person Y’s speed increases by 0.25 km/hr every hour:
Hour 1: 1.0 km/hr
Hour 2: 1.25 km/hr
Hour 3: 1.5 km/hr
Hour 4: 1.75 km/hr
Hour 5: 2.0 km/hr

Step 1: Calculate X’s distance in 5 hours
– X’s distance = Speed × Time
– X’s distance = 1.5 × 5 = 7.5 km

Step 2: Calculate Y’s total distance in 5 hours
– Hour 1: 1.0 km
– Hour 2: 1.25 km
– Hour 3: 1.5 km
– Hour 4: 1.75 km
– Hour 5: 2.0 km
Total = 7.5 km

Step 3: Verify statements
1. They take 5 hours to meet
– Total distance covered = X’s distance + Y’s distance
– 7.5 + 7.5 = 15 km (complete distance)
– Therefore, they meet in 5 hours (True)

2. They meet midway
– Both cover 7.5 km each
– 7.5 km is exactly half of 15 km
– Therefore, they meet midway (True)

Answer: Option (c) Both statements 1 and 2 are correct.

Q. A person X from a place A and another person Y from a place B set out at the same time to walk towards each other. Read More »

Q. You are given two identical sequences in two rows: Sequence-I: 8 4 6 15 52.5 236.5 Sequence-II: 5 A B C D E

Q. You are given two identical sequences in two rows:

Sequence-I: 8 4 6 15 52.5 236.5
Sequence-II: 5 A B C D E

What is the entry in the place of C for the Sequence-II?
(a) 2.5
(b) 5
(c) 9.375
(d) 32.8125
Correct Answer: (c) 9.375

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

8 4 6 15 x 236.25

Let us solve this step by step:

Sequence I:
Let us start with 8:
8 × 0.5 → 4
4 × 1.5 → 6
6 × 2.5 → 15
15 × 3.5 → 52.5
52.5 × 4.5 → 236.25

Sequence II:
Let us start with 5:
5 × 0.5 → 2.5 (A)
2.5 × 1.5 → 3.75 (B)
3.75 × 2.5 → 9.375 (C)

Let us observe the pattern:
The multipliers increase by 1 each time:
0.5, 1.5, 2.5, 3.5, 4.5

Q. You are given two identical sequences in two rows: Sequence-I: 8 4 6 15 52.5 236.5 Sequence-II: 5 A B C D E Read More »

Q. Following is a matrix of certain entries. The entries follow a certain trend row-wise. Choose the missing entry (?) accordingly.

Q. Following is a matrix of certain entries. The entries follow a certain trend row-wise. Choose the missing entry (?) accordingly.

7B 10A 3C
3C 9B 6A
10A 13C ?

(a) 9B
(b) 3A
(c) 3B
(d) 3C
Correct Answer: (c) 3B

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

7b 10a 3c

Row 1 : 10 – 7 = 3
Row 2 : 9 – 3 = 3
Row 3 = 13 – 10 = 3, B was missing in row 3

Q. Following is a matrix of certain entries. The entries follow a certain trend row-wise. Choose the missing entry (?) accordingly. Read More »