Page 6 - Services Selection Board (SSB) Interviews

2 Number Series Completion
Solution: The given series is in the pattern × 2, × 3/2, × 2, × 3/2, ×2,.....

1 2 3 6 9 18 ? 54
So, the missing term is 18 × 3/2 = 27 Or
+1 +1 +3 +3 +9 +9 +27
1 1 × 3 3 × 3 9 × 3
Ans: (b) 27
Pattern 4: When a series follows the following pattern add, multiply, add, multiply, add,.... or add, substract, add,
substract, add,.... etc.
Ex 6: 4, 6, 12, 14, 28, 30, .....

4 6 12 14 28 30 60
Solution:
+2 ×2 +2 ×2 +2 ×2
60 is the next number
Ex 7: 8, 28, 116, 584, ? (R.R.B 2002)
(a) 1752 (b) 3502 (c) 3504
(d) 3508 (e) None of these

Solution: The given series is in the pattern: × 3 + 4, × 4 + 4, × 5 + 4, .....
(8 × 3) + 4 = 28
(28 × 4) + 4 = 116
(116 × 5) + 4 = 584
(584 × 6) + 4 = 3508
So, the missing term is 584 × 6 + 4 = 3508.
Ans: Option (d)
Ex 8: 3 4 10 33 136 685 ?
(a) 3430 (b) 4802 (c) 5145
(d) 4116 (e) 5488

Solution: In this particular Series, the pattern is-
3 × 1 + 1 = 4; 4 × 2 + 2 = 10; 10 × 3 + 3 = 33; 33 × 4 + 4 = 136; 136 × 5 + 5 = 685; 685 × 6 + 6 = 4116.
Hence option (d)

Pattern 5: Series with Square or cube or square root or cube root of the number.
Ex 9: 1, 9, 25, 49, ?, 121 (S.S.C.)
(a) 64 (b) 81 (c) 91
(d) 100 (e) None of these
2
2
2
2
Solution: The given series consists of squares of consecutive odd numbers i.e 1 , 3 , 5 , 7 ,.....
2
So, the missing term = 9 = 81
Ans: Option (b)
Pattern 6: TRIANGULAR NUMBER
th
When any number series is in the form a, a + (a +1), a+ (a+1)+ (a+2), a + (a+1)+ (a+2) + (a+3), ........., n term
 n n )1  15 (15 1 ) +
( +
of the series be   . =  
 2   2 
th
Ex 10: 1, 3, 6, 4, 15, 21, ...... find the 15 term of the series?
 n n )1  15 (15 1 ) +
( +
th
Solution : 15 term =   =   = 120 where n = 15.
 2   2 