வெல்லுங்கள் CSAT 2025 - 23: Number Series

Questions & Answers- (Multiple Choice) - Number Series
கொள்குறி வினா- விடைகள் - எண்கள்- தொடர்கள்

1 - 3 In the following series, what number should replace the '?' ?

1. 2, 7, 14, 23, ?, 47
a. 33 b. 34
c. 35 d. 36

2 . 4, 6, 12, 14, 28, 30, ?
a. 32 b. 62
c. 60 d. 64

3. 7, 6, 13, 19, 32, ? , 83
a. 51 b. 53
c. 61 d. 64

4 - 7 In the following series, find the
odd man out.

4. 11, 13, 17, 19, 23, 25, 29, 31, 37, 41
a. 23 b. 31
c. 25 d. 41

5. 15, 31, 63, 127, 253, 511
a. 63 b. 253
c. 127 d. 511

6. 9, 12, 11, 14, 13, 16, 15 , 17
a. 14 b. 15
c. 16 d. 17

7 . 0.5, 0.55, 0.65, 0.75, 0.85
a. 0.5 b. 0.55
c. 0.75 d. 0.85

8 - 11 Find next two numbers in the following series.

8. 1, 8, 9, 64, 25, 216 , ? , ?
a. 49, 64 b. 343, 512
c. 49, 512 d. 343, 64

9. 6, 11, 21, 36, 56, _ , _
a. 76, 96 b. 81, 111
c. 76, 101 d. 81, 106

10. 48, 24, 42, 21, 36, 18, 30, __ , __
a. 15, 24 b. 24, 15
c. 15, 25 d. 16, 24.

11. 35, 28, 22, 17, 13, 10, 8, __ , __
a. 7, 6 b. 9, 7
c. 7, 7 d. 8, 7

12 - 15 One number is wrong in all the following series. Identify the wrong one and choose the correct number in that place.

12. 3, 5, 7, 11, 15, 17, 19
a. 13 b. 9
c. 18 d. 12

13. 13, 35, 57, 79, 91, 123
a. 133 b. 97
c. 101 d. 103

14. 2197, 1728, 1332, 1000, 729, 512
a. 728 b. 1331
c. 1001 d. 2198

15. 253, 374, 682, 594, 472, 781
a. 642 b. 624
c. 246 d. 462

16 - 20 In the following, write the missing term using the rules applied in each question.

16. 24 4 92
33 2 64
19 3 ?
a. 54 b. 57
c. 60 d. 51

17. 12 9 2 19
10 7 ? 14
11 8 6 13
a. 4 b. 3
c. 6 d. 5

18. 8 1 641
9 5 815
5 2 252
11 3 ?
a. 643 b. 1483
c. 1213 d. 819

19. 2 3 35
3 4 91
5 6 ?
a. 54 b. 57
c. 60 d. 341

20. 8 3 55
7 4 ?
10 5 75
a. 33 b. 35
c. 36 d. 45

Answers

1. b 2. c 3. a 4. c 5. b

6. d 7. a 8. c 9. b 10. a

11. c 12. a 13. c 14. b 15. d

16. a 17. b 18. c 19. d 20. a

Explanation to Answers

1. 2, 7, 14, 23, ?, 47
Diff 5 7 9 11 13
2 + 5 = 7 ; 7 + 7 = 14 ; 14 + 9 = 23 ;
23 + 11 = 34 ; 34 + 13 = 47
Correct answer is 34.

2. 4, 6, 12, 14, 28, 30, ?
Diff + 2 ×2 +2 ×2 +2 ×2
So answer must be 30 × 2 = 60.

3. 7 + 6 = 13 ; 6 + 13 = 19 ; 13 + 19 = 32 ;
19 + 32 = 51 ; 32 + 51 = 83
Fibonacci series
Third term is addition of first two numbers. Fourth term is addition of previous two terms and so on.
Hence the correct answer is 51.

4. All are prime numbers except 25.
So 25 is the odd man out.

5. 15×2 +1 = 31 ; 31×2+1 = 63 ;
63×2+1 = 127 ; 127×2+1 = 255;
255×2+1 = 511
Wrong number is 253.

6. 9 12 11 14 13 16 15 17
Diff 3 -1 3 -1 3 -1 2
It is clear that 17 is odd man out.
Correct number is 18.

7. 0.5 0.55 0.65 0.75 0.85
Diff 0.05 0.10 0.10 0.10
Here 0.5 is odd man out.
Correct must be 0.55 - 0.10 = 0.45

8. Split into two series taking alternate terms, 1, 9, 25, ? and 8, 64, 216, ?
In the first series, 1, 9, 25, ?
1^2 = 1 ; 3^2 = 9 ; 5^2 = 25 ;
Next term must be 7^2 = 49
In the second series, 8, 64, 216, ?
2^3 = 8 ; 4^3 = 64 ; 6^3 = 216 ;
Next term must be 8^3 = 512
So answer must be 49, 512.

9. 6, 11, 21, 36, 56, _ , _
Diff 5 10 15 20 25 30
So next two numbers are
56 + 25 = 81 and
81 + 30 = 111

10. Spliting into two series,
I. 48, 42, 36, 30, _
II. 24, 21, 18, _
48 42 36 30 _
Diff -6 -6 -6 -6
So 30 - 6 = 24 is the next number.
24 21 18 _
Diff - 3 - 3 - 3
Therefore 18 - 3 = 15 is the next number.
Next two numbers are 15 and 24.

11. 35 28 22 17 13 10 8 __ __
Diff -7 - 6 - 5 - 4 - 3 - 2 - 1 - 0
So next two numbers are 8 - 1 = 7 and
7 - 0 = 7
Hence next two numbers are 7 and 7.

12. Except 15 all other numbers are sequential primes. But 15 is a composite number.
After 11, the prime number is 13.
Correct number in the place of 15 is 13.

13. 13 35 57 79 91 123
Diff 22 22 22 12 32
Here upto 79, the series is in correct way of adding 22 to the previous term. After 79, the number must be 79+22 = 101.
So 91 is wrong and the correct number in that place is 101.
After that 101 + 22 = 123 which is correctly placed.

14. All are cube numbers except 1332.
2197 = 13^3 ; 1728 = 12^3 ;
1331 = 11^3 ; 1000 = 10^3 ;
729 = 9^3 ; 512 = 8^3
So 1332 is wrong. Correct number is 1331.

15. In each term middle digit is the sum of other two digits except 472.
253 -> 2+3 = 5 ; 374 -> 3+4 = 7; etc.,
But 472 must be 462 whereas 4+2 = 6.
So 472 is wrong. But correct number must be 462.

16. 24 × 4 - 4 = 96 - 4 = 92
33 × 2 - 2 = 66 - 2 = 64
So 19 × 3 - 3 = 57 - 3 = 54.

17. 12 + 9 - 2 = 19
10 + 7 - ? = 14, so ? = 3
11 + 8 - 6 = 13
So correct answer is 3.

18. 8 1 (8^2)1 = 641
9 5 (9^2)5 = 815
5 2 (5^2)2 = 252
So 11 3 (11^2)3 = 1213.

19. (2×2 + 3)×(2+3) = 7×5 = 35
(3×3 + 4)×(3+4) = 13×7 = 91
In the same rule
(5×5 + 6)×(5+6) = 31×11 = 341

20. 8×8 - 3×3 = 64 - 9 = 55
10×10 - 5×5 = 100 - 25 = 75
So 7×7 - 4×4 = 49 - 16 = 33.

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