3.

Number Series Questions 21–30

Find the Missing Number with Step-by-Step Logic

Directions: What will come in place of question mark (?) in the following series?

21.

489 510 516 528 543 555 ?

Pattern: +21, +6, +12, +15, +12, +15 → alternating +12 and +15 after first jump

A. 569

B. 570

C. 573

D. 568

E. None of these

C. 573
555 + 18 = 573 (pattern: +21, +6, +12, +15, +12, +15, +18 → increasing by 3)

22.

81 91 109 146 221 351 ?

Pattern: +10, +18, +37, +75, +130, +208 → differences increase by ×2 –2

A. 578

B. 582

C. 591

D. 576

E. None of these

A. 578
351 + 227 = 578 (differences: 10,18,37,75,130,208,227 → +8,+19,+38,+55,+78,+19)

23.

540 538 534 526 510 ? 414

Pattern: –2, –4, –8, –16, –32, –64 → halving each time

A. 470

B. 478

C. 474

D. 472

E. None of these

B. 478
510 – 32 = 478 → 478 – 64 = 414

24.

32 24 20 18 17 ?

Pattern: –8, –4, –2, –1, –0.5 → halving the subtraction

A. 16.5

B. 8.5

C. 12.5

D. 18.5

E. None of these

A. 16.5
17 – 0.5 = 16.5

25.

1 3 9 39 249 2559 ?

Pattern: ×3, ×3, ×4 +3, ×6 +3, ×10 +9 → Fibonacci-like

A. 28561

B. 30458

C. 32589

D. 35289

E. None of these

A. 28561
2559 × 11 + 18 = 28149 + 412 = 28561 (pattern: ×n + (n-1)×3)

26.

704 88 22 8.25 ?

Pattern: ÷8, ÷4, ÷2.666..., ÷2.5 → decreasing divisor

A. 4.125

B. 6.50

C. 6.25

D. 5.25

E. None of these

A. 4.125
8.25 ÷ 2 = 4.125

27.

2 10 30 68 130 ?

Pattern: ×5, ×3, ×2 +8, ×2 –6, ×2 +4 → alternating

A. 221

B. 230

C. 222

D. 225

E. None of these

C. 222
130 × 1.7 + 1 = 221 +1 = 222 (pattern: ×5,×3,×2+8,×1.9+6,×1.7+4)

28.

1 4 15 28 57 88 ?

Pattern: +3, +11, +13, +29, +31, +43 → +prime numbers with gap

A. 133

B. 143

C. 157

D. 147

E. None of these

A. 133
88 + 45 = 133 (differences: 3,11,13,29,31,45 → +8,+2,+16,+2,+14)

3

29.

122 171 228 293 366 ?

Pattern: +49, +57, +65, +73, +81 → +8 each time

A. 450

B. 455

C. 447

D. 465

E. None of these

C. 447
366 + 81 = 447 (differences: 49,57,65,73,81 → +8 each)

30.

13 15 19 27 43 ?

Pattern: +2, +4, +8, +16, +32 → powers of 2

A. 74

B. 72

C. 73

D. 75

E. None of these

D. 75
43 + 32 = 75 (next would be +64)

© 2025 Number Series Practice | Questions 21–30 with Logic Diagrams