Quiz on Series

Topic: Series and odd one out:

Directions (1-5): Find the wrong one in the series

1.      4, 5, 15, 49, 201, 1011, 6073

(a) 5                            (b) 15

    (c) 49                          (d) 201

    (e) 1011

2.      888, 440, 216, 104, 48, 22, 6

(a) 440                        (b) 216

(c) 104                        (d) 48

(e) 22

3.      2, 3, 6, 15, 52.5, 157.5, 630

(a) 3                            (b)6

(c) 15                          (d) 52.5

(e) 157.5

4.      5, 8, 20, 42, 124, 246, 736

(a) 8                            (b) 20

(c) 42                          (d) 124

(e) 246

5.      1050, 510, 242, 106, 46, 16, 3

(a) 510                        (b) 242

(c) 106                        (d) 46

(e) 16

Directions (6-10): Insert the missing number

6.      9, 12, 11, 14, 13, ___, 15

(a) 12                    (b) 16

(c) 10                    (d) 17

7.      71, 76, 69, 74, 67, 72, ___

(a) 77                    (b) 65

(c) 80                    (d) 76

8.      10, 5, 13, 10, 16, 20, 19, ___

(a) 22                    (b) 40

(c) 38                    (d) 23

9.      7, 26, 63, 124, 215, 342, ___

(a) 481                  (b) 511

(c) 391                  (d) 421

10.   165, 195, 255, 285, 345, ___

(a) 375                  (b) 420

(c) 435                  (d) 390

Answers:

1	a	6	b
2	e	7	b
3	d	8	b
4	b	9	b
5	c	10	c

Solutions:

1.      2^ndterm = (1^st term *1+2)= (4*1+2) = 6

3^rd term = (2^ndterm*2+3) = (6*2+3) = 15

4^th term = (3^rdterm*3+4) = (15*3+4) = 49

5^th term = (4^thterm*4+5) = (49*4+5) = 210 and so on

Therefore 5 is wrong

2.      2^ndterm = (1^st term - 8)/2 = (888-8)/2 = 440

3^rd term = (2^stterm - 8)/2 = (440-8)/2 = 216

4^rd term = (3^stterm - 8)/2 = (216-8)/2 = 104

5^rd term = (4^stterm - 8)/2 = (104-8)/2 = 48

6^rd term = (5^stterm - 8)/2 = (48-8)/2 =20

Therefore 22 is wrong

3.      2^ndterm = (1^st term* 1.5) = 2 * 1.5 = 3

3^rd term = (2^stterm* 2) = 3* 2 = 6

4^th term = (3^stterm* 2.5) = 6 * 2.5 = 15

5^th term = (4^stterm* 3) = 15 * 3 = 45

Therefore 52.5 is wrong

4.      2^ndterm = (1^st term * 2 - 2) = (5 * 2 – 2)  = 8

3^rd term = (2^stterm * 3 - 2 ) = (8* 3 – 2) = 22

4^th term = (3^stterm * 2 - 2 ) = (22 * 2 – 2) = 42

5^th term = (4^stterm * 3 - 3) = (42 * 3 – 2) = 124 and so on

Therefore 20 is wrong

5.      2^ndterm = (1^st term - 30)/2= (1050-30)/2= 510

3^rd term = (2^stterm - 26)/2= (510-26)/2= 242

4^th term = (3^stterm - 22)/2 = (242-22)/2 = 110

Therefore 106 is wrong

6.      Alternatively, We add 3 and subtract 1

7.      Alternatively, We add 5 and subtract 7

8.      There are two series (10, 13, 16, 19) and (5, 10, 20, 40), one increasing by 3 and the other multiplied by 2

9.      Numbers are (2³ - 1), (3³ - 1), (4⁴ - 1), (5³- 1) etc…… so, the next no. is (8³ - 1) = 512- 1 = 511

10.   Each number is 15 multiplied by a prime number i.e., 15 * 11, 15 * 13, 15 * 17, 15 * 19 and so on

So the next number is 15 * 29 = 435