Number Series – Hard Level Questions – UGC NET Paper 1

Q1): Find the next term in the series: 1, 4, 12, 32, 80, ?
A) 190
B) 192
C) 194
D) 196

Answer: B) 192
Explanation: Each term is formed by multiplying the previous term by 2 and then adding a number that doubles each time.
1×2+2=4, 4×2+4=12, 12×2+8=32, 32×2+16=80.
Next, add 32 (because 2, 4, 8, 16, 32 are doubling).
So, 80×2+32 = 160+32 = 192.


Q2): Find the missing term in the series: 2, 5, 4, 9, 8, 13, 16, __, 32
A) 15
B) 16
C) 17
D) 18

Answer: C) 17
Explanation: This is an interleaved (two-pattern) series.
Odd positions: 2, 4, 8, 16, 32 (each term is ×2).
Even positions: 5, 9, 13, 17 (each term is +4).
So the missing even-position term after 13 is 13+4 = 17.


Q3): Identify the wrong term in the series: 1, 2, 6, 24, 120, 600, 5040
A) 24
B) 120
C) 600
D) 5040

Answer: C) 600
Explanation: These numbers are factorials:
1! = 1, 2! = 2, 3! = 6, 4! = 24, 5! = 120.
The next should be 6! = 720, and then 7! = 5040.
But the series has 600 instead of 720, so 600 is the wrong term.


Q4): Find the next term in the series: 1, 2, 5, 12, 29, 70, ?
A) 168
B) 169
C) 170
D) 171

Answer: B) 169
Explanation: Each term follows the rule: next = (2 × previous term) + term before previous.
Check: 2×2 + 1 = 5, 2×5 + 2 = 12, 2×12 + 5 = 29, 2×29 + 12 = 70.
So next = 2×70 + 29 = 140 + 29 = 169.


Q5): Find the missing term in the series: 6, 13, 23, 36, 52, __, 93
A) 69
B) 70
C) 71
D) 72

Answer: C) 71
Explanation: Look at the differences:
13−6=7, 23−13=10, 36−23=13, 52−36=16.
The differences increase by +3 each time (7, 10, 13, 16).
Next difference = 19, so missing term = 52 + 19 = 71.
Then next difference = 22, and 71 + 22 = 93, which matches.


Q6): Find the next term in the series: 2, 5, 14, 37, 90, 205, ?
A) 442
B) 444
C) 446
D) 448

Answer: C) 446
Explanation: The rule is: next = (2 × previous) + square numbers in order.
2×2 + 1² = 5
2×5 + 2² = 14
2×14 + 3² = 37
2×37 + 4² = 90
2×90 + 5² = 205
So next = 2×205 + 6² = 410 + 36 = 446.


Q7): Identify the wrong term in the series: 4, 2, 9, 3, 16, 5, 25, 7, 35, 11
A) 25
B) 7
C) 35
D) 11

Answer: C) 35
Explanation: The series alternates between perfect squares and prime numbers.
Squares: 4, 9, 16, 25, 36
Primes: 2, 3, 5, 7, 11
So the term before 11 should be 36 (a square), but 35 is given. Hence 35 is the wrong term.


Q8): Find the next term in the series: 50, 47, 52, 45, 56, 43, ?
A) 58
B) 59
C) 60
D) 61

Answer: C) 60
Explanation: The pattern uses consecutive prime numbers with alternating subtraction and addition.
50−3=47, 47+5=52, 52−7=45, 45+11=56, 56−13=43.
Next we add the next prime 17: 43 + 17 = 60.


Q9): Find the missing term in the series: 2, 3, 7, 8, 14, 15, __, 24, 34
A) 22
B) 23
C) 24
D) 25

Answer: B) 23
Explanation: The pattern repeats in pairs: “+1” then “+even number increasing by 2.”
2+1=3, then +4=7
7+1=8, then +6=14
14+1=15, then +8=23
23+1=24, then +10=34
So the missing term is 23.


Q10): Identify the wrong term in the series: 3, 8, 15, 24, 36, 48, 63
A) 8
B) 24
C) 36
D) 63

Answer: C) 36
Explanation: The pattern is n² − 1:
2²−1=3, 3²−1=8, 4²−1=15, 5²−1=24, 6²−1=35, 7²−1=48, 8²−1=63.
So the term should be 35, but 36 is written. Hence 36 is the wrong term.


Q11): Find the next term in the series: 1, 4, 10, 20, 35, ?
A) 54
B) 55
C) 56
D) 57

Answer: C) 56
Explanation: Look at the differences:
4−1=3, 10−4=6, 20−10=10, 35−20=15.
These are triangular numbers: 3, 6, 10, 15 (adding 3, then 6, then 10, then 15).
Next triangular number is 21.
So next term = 35 + 21 = 56.


Q12): Find the next term in the series: 100, 98, 101, 96, 103, 92, 105, ?
A) 87
B) 88
C) 89
D) 90

Answer: B) 88
Explanation: The series alternates subtraction and addition of consecutive primes.
100−2=98, 98+3=101, 101−5=96, 96+7=103, 103−11=92, 92+13=105.
Next we subtract the next prime 17: 105 − 17 = 88.


Q13): Find the missing term in the series: 1, 2, 6, 15, 31, __, 92
A) 54
B) 55
C) 56
D) 57

Answer: C) 56
Explanation: The differences are perfect squares:
2−1=1 (=1²)
6−2=4 (=2²)
15−6=9 (=3²)
31−15=16 (=4²)
Next difference should be 25 (=5²).
So missing term = 31 + 25 = 56.
Then 92 − 56 = 36 (=6²), which matches the next square difference.


Q14): Identify the wrong term in the series: 2, 9, 28, 65, 125, 217
A) 28
B) 65
C) 125
D) 217

Answer: C) 125
Explanation: The pattern is n³ + 1:
1³+1=2, 2³+1=9, 3³+1=28, 4³+1=65, 5³+1=126, 6³+1=217.
So the term should be 126, but 125 is given. Hence 125 is the wrong term.


Q15): Find the missing term in the series: 12, 33, 66, 132, __, 726
A) 353
B) 363
C) 373
D) 383

Answer: B) 363
Explanation: Each next term = number + reverse of the number.
12 + 21 = 33
33 + 33 = 66
66 + 66 = 132
132 + 231 = 363
363 + 363 = 726
So the missing term is 363.


Q16): Find the next term in the series: 0, 6, 24, 60, 120, ?
A) 204
B) 210
C) 216
D) 220

Answer: B) 210
Explanation: The pattern is n³ − n starting from n=1:
1³−1=0
2³−2=6
3³−3=24
4³−4=60
5³−5=120
Next is 6³−6 = 216−6 = 210.


Q17): Find the missing term in the series: 7, 16, 36, 78, __, 222
A) 142
B) 143
C) 144
D) 145

Answer: C) 144
Explanation: Each term is (product of consecutive primes) + 1.
2×3+1=7
3×5+1=16
5×7+1=36
7×11+1=78
11×13+1=144
13×17+1=222
So the missing term is 144.


Q18): Find the next term in the series: 2, 6, 7, 21, 24, 72, 77, ?
A) 228
B) 229
C) 231
D) 233

Answer: C) 231
Explanation: The series follows a repeating two-step pattern: multiply by 3, then add an odd number that increases by 2.
2×3=6, +1=7
7×3=21, +3=24
24×3=72, +5=77
Next step is multiplication by 3: 77×3 = 231.


Q19): Identify the wrong term in the series: 3, 5, 9, 17, 31, 65
A) 3
B) 9
C) 31
D) 65

Answer: C) 31
Explanation: The pattern is 2ⁿ + 1:
2¹+1=3, 2²+1=5, 2³+1=9, 2⁴+1=17, 2⁵+1=33, 2⁶+1=65.
So the fifth term should be 33, but 31 is given. Hence 31 is the wrong term.


Q20): Find the missing term in the series: 2, 10, 12, 60, 62, __, 312
A) 308
B) 309
C) 310
D) 311

Answer: C) 310
Explanation: The pattern alternates between “×5” and “+2.”
2×5=10, 10+2=12, 12×5=60, 60+2=62, 62×5=310, 310+2=312.
So the missing term is 310.

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