UPSC PRELIMS EXAMINATION 2021, CSAT PAPER -2 MATHS MENTAL ABILITY SOLVED QUESTIONS By Kumar B Bagival.

UPSC PRELIMS EXAMINATION CSAT PAPER -2 

MATHS MENTAL ABILITY SOLVED QUESTIONS 

1. Seven books P,Q,R,S,T,U,and V, are placed side by side. R,Q and T have blue covers and other books have red covers. Only S and U are new books and the rest are old. P,R,and S are law reports; the rest are gazetteers. Books of old gazetteers with blue covers are

1. Q and R

2. Q and U

3. Q and T

4. T and U

Solution: 

P - Red , old, law report.

Q - Old, blue, gazetteers

R - Old, blue, law report

S - New, red , law report

T - Old, blue, gazetteers

U - New, red, gazetteers

V - Old, red , gazetteers

Therefore Q and T old gazetteers having blue cover.

So answer is 

(C) Q and T

2.  Replace the incorrect term by  correct term in the given sequence

3,2,7,4,13,10,21,18,31,28,43,40

Where odd terms and even terms follow the same pattern.

1. 0

2. 1

3. 3

4. 6

Solution : 

Odd terms are 3, 7, 13, 21, 31, 43

So gap between each pair is like

      43-31= 12

      31-21= 10

       21-13= 8

       13-7= 6

       7-3= 4

Even terms are 2, 4, 10,18,28,40

So gap between each pair is 

       40-28= 12

       28-18= 10

       18-10= 8

       10-4 = 6

        4-2= 2 here last pair cannot match with Odd numbers pattern here it may come like

4-0=4

So instead of 2, 0 is the correct term.

So answer is

 

1.  0C

3 . 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	?

1. 9B

2. 3A

3. 3B

4. 3C

Solution : Here in first row 7B + 3C = 10A

                            Second row 3C + 6A = 9B

                            Third row 10A + ? = 13 C

          10A + ? = 13C

                     ? = 13C - 10A

                     ? = 3B

Here A, B, and C are cyclic.

So the answer is  

         (C) 3B

4. You are give two identical sequences in two rows:

Sequence |	8	4	6	15	52.5	236.25
Sequence ||	5	A	B	C	D	E

What is the entry in the place of C for the sequence-||

1. 2.5

2. 5

3. 9.375

4. 32.8125

Solution : In sequence- | , 8,4, 6, 15, 52.5, 236.25

               That is   8×0.5 = 4

                             4 ×1.5 = 6

                             6×2.5 = 15

                             15×3.5= 52.5

                              52.5×4.5= 236.25

Similarly in Sequence-|| also

                             5×0.5=2.5= A

                             2.5×1.5= 3.75= B

                             3.75×2.5= 9.375 = C

                             9.375×3.5= 32.8125 =D

                             32.8125×4.5= 142.65625

So the answer is 

                 (C) 9.375

               

5 . 3^2019 is divided by 10 then what is the remainder.

1. 1

2. 3

3. 7

4. 9

Solution : last two digit of the power that is divide by 4 we get remainder 3

Hence 3^3 we get that is 3×3×3=27

So remainder is 7

Answer is.   (C)7 

6. The number 3798125P369 is divisible by 7. What is the value of the digit P?

1. 1

2. 6

3. 7

4. 9

Solution : Divisibility by 7 is 

              Number we get from the Number formed by the last 3 digits of the given number is subtracted from the number formed by the rest digit must be 0 or divisible by 7.

 Hence  If we put P=6

                37981256369 ÷7 = 542841

So the answer is 

                (B)6

                

7. From January 1st, 2021, the price of petrol ( in rupees per litre) on the mth day of the year is 80+0.1m, where m= 1,2,3,4,.....,100. And thereafter remains constant. On the other hand the price of diesel ( in rupees per litre) on nth day of 2021 is 69+0.15n for any n. On which date in the year 2021, are the price of these two fuels equal.

1. 21st May

2. 20th May

3. 19th May

4. 18th May

Solution : Price of petrol on mth day

               Let m= 100

            P= 80+ (0.1×100)

               = 80+10

               = 90₹

           Price of Diesel on nth day.            

               Let n= 100.                              

             D= 69+0.15n.

         Then    P= D

                   90= 69+(0.15n)                                   

                90-69= 0.15n                                                

                     21= 0.15n                                                 

                   21/0.15= 140            

Jan - 31+Feb-28+March-31+April-30+May20= 140days

 So answer is 

(B) 20th May

                                 

     

8. A biological class at high school predicted that a local population of animals  will double in size every twelve years. The population at the beginning of the year  2021 was estimated to be 50 animals. If P represents the population after n years, which one of the following equations  represents the model of the class for the population.

1. P = 12+50n

2. P = 50+12n

3. P = 50(2)^12n

4. P = 50(2)^n/12

Solution: 

Directly we can say P= 50(2)^n/12

Answer is.   

(D)P=50(2)^n/12

9. In a class 60% of the 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?

     

1. 45%

2. 40%

3. 30%

4. 20%

Solution : Let total students be 100

             Indian students = 60%of 100 = 60

             Girls = 50% of 100 = 50

             Boys = 50

30% of Indian students are girls = 30%of 60 = 18

So Indian boys are = 60-18 = 42

So foreign Boys are = 50 - 42 = 8

Hence percentage of foreign boys are 

= 8÷40× 100= 20%

Answer is (D) 20%

10. In a group of 120 persons, 80 are Indians and the rest are foreigners. Furthermore, 70 people in the group can speak English. The number of Indians who can speak English is.

1. 20

2. 30

3. 30 or less

4. 30 or more

Solution : 

                 Total = 120

           Indians.  = 80

        Foreigners = 40

People can speak English = 70

If 40 foreigners can speak English then 30 Indians can speak English, or if No foreigners can speak English 70 Indians can speak  English. So 30/or more Indians can speak English.

 

So answer is  (D) 30 or more

-Solved By 

Kumar B Bagival

Continued....... In next part.