Question 1

120, 99, 80, 63, 48,?

Accepted Answer

The pattern is - 21, - 19, - 17, - 15,..... So, missing term = 48 - 13 = 35.

Question 2

589654237, 89654237, 8965423, 965423,?

Accepted Answer

The digits are removed one by one from the beginning and the end in order alternately so as to obtain the subsequent terms of the series.

Question 3

3, 10, 101,?

Accepted Answer

Each term in the series is obtained by adding 1 to the square of the preceding term. So, missing term = (101)2 + 1 = 10202.

Question 4

In the series 2, 6, 18, 54, ...... what will be the 8th term?

Accepted Answer

Clearly, 2 x 3 = 6, 6 x 3 = 18, 18 x 3 = 54,..... So, the series is a G.P. in which a = 2, r = 3. Therefore 8th term = ar8-1 = ar7 = 2 x 37 = (2 x 2187) = 4374.

Question 5

125,80,45,20,?

Accepted Answer

The pattern is - 45, - 35, - 25, ..... So, missing term = 20 - 15 = 5.

Question 6

1, 1, 4, 8, 9, 27, 16,?

Accepted Answer

The series consists of squares and cubes of consecutive natural numbers i.e. 12, 13, 22, 23, 32, 33, 42, ..... So, missing term = 43 = 64.

Question 7

1, 2, 3, 6, 9, 18,?, 54

Accepted Answer

The pattern is x 2, x 3/2, x 2, x 3/2, x 2,..... So, missing term = 18 x 3/2 = 27.

Question 8

6, 13, 25, 51, 101,?

Accepted Answer

The pattern is x 2 + 1, x 2 - 1, x 2 + 1, x 2 - 1,..... So, missing term = 101 x 2 + 1 = 203.

Question 9

5,6,9, 15,?, 40

Accepted Answer

The pattern is + 1, + 3, + 6,....., i.e. + 1, + (1, + 2), + (1 + 2 + 3),..... So, missing term = 15 + (1 + 2 + 3 + 4) = 25.

Question 10

1, 3, 4, 8, 15, 27,?

Accepted Answer

The sum of any three consecutive terms of the series gives the next term. So, missing number = 8 + 15 + 27 = 50.

Question 11

3, 4, 7, 7, 13, 13, 21, 22, 31, 34,?

Accepted Answer

The given sequence is a combination of two series : I. 3, 7, 13, 21, 31, ? and II. 4, 7, 13, 22, 34 The pattern in I is + 4, + 6, + 8, + 10,..... The pattern in II is + 3, + 6, + 9, + 12,..... So, missing term = 31 + 12 = 43.

Question 12

198, 194, 185, 169,?

Accepted Answer

The pattern is - 4, - 9, - 16,.....i.e. - 22, - 32, - 42,..... So, missing pattern = 169 - 52 = 169 - 25 = 144.

Question 13

2, 3, 5,7,11,?, 17

Accepted Answer

Clearly, the given series consists of prime numbers starting from 2. So, the missing term is the prime number after 11, which is 13.

Question 14

6, 12, 21,?, 48

Accepted Answer

The pattern is + 6, + 9, + 12, + 15, ..... So, missing term = 21 + 12 = 33.

Question 15

Which term of the series 5, 10, 20, 40, ..... is 1280?

Accepted Answer

Clearly, 5 x 2 = 10, 10 x 2 = 20, 20 x 2 = 40,..... So, the series is a G.P. in which a = 5 and r = 2. Let 1280 be the rath term of the series. Then, 5x2n-1 = 1280 ⟺ 2n-1 = 256 = 28 ⟺ n - 1 = 8 ⟺ n = 9.

Question 16

2, 5, 9,?, 20, 27

Accepted Answer

The pattern is + 3, + 4, + 5, + 6,..... So, missing term = 9 + 5 = 14.

Question 17

2, 3, 3, 5, 10, 13,?, 43, 172, 177

Accepted Answer

The pattern is + 1, x 1, + 2, x 2, + 3, x 3, + 4, x 4, + 5. So, missing term = 13 x 3 = 39.

Question 18

9, 27, 31, 155, 161, 1127,?

Accepted Answer

The pattern is x 3, + 4, x 5, + 6, x 7,..... So, missing term = 1127 + 8 = 1135.

Question 19

2, 1, 2, 4, 4, 5, 6, 7, 8, 8, 10, 11,?

Accepted Answer

The given sequence is a combination of three series : I. 1st, 4th, 7th, 10th, 13th terms i.e. 2, 4, 6, 8, ? II. 2nd, 5th, 8th, 11th terms i.e. 1, 4, 7, 10 III. 3rd, 6th, 9th, 12th terms i.e. 2, 5, 8, 11 Clearly, I consists of consecutive even numbers. So, the missing term is 10.

Question 20

Which of the following will not be a number of the series 1, 8, 27, 64, 125,.....?

Accepted Answer

The given series consists of cubes of natural numbers only. 256 is not the cube of any natural number.

Series Completion Questions