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SPEEDY Railway Book (English)

Number Series Questions for IBPS PO Exams

Number Series Questions for IBPS PO Exams
Number Series Questions with Solution

Directions (Q.1 – Q.10): In each of the following series only one no is wrong. Find out that wrong number.
Q.1        6      9.5       20       51.5        155         550.25
a). 9.5
b). 550.25
c). 20
d). 155
e).None of these

Q.2       18        19        27        54       117        243
a). 19
b). 27
c). 243
d). 117
e). None of these.

Q3.      14       28        80       576        8960        285696
a). 28
b). 14
c). 576
d). 285696
e) None of these.

Q4.       44     22       62      33        99       44.5         133.5
a). 44
b). 62
c). 133.5
d) 99
e) None of these.

Q.5    7      14     37         77      157         317
a). 37
b). 157
c). 317
d). 14
e) None of these.

Q.6    7         7      13       39       97         217
a). 13
b). 97
c). 39
d). 217
e) None of these.

Q.7      2       9       30      105      420       2195       13182 
a).9 
b). 420 
c).105 
d). 13182 
e) None of these.

Q.8.    10       19       57        223       1111        6671 
a). 19 
b). 1111 
c). 57 
d). 6671 
e). None of these.

Q.9.    36       18         27        81        236.25         1063.125 
a).81
b). 36
c).236.25
d). 1063.125
e). None of these.

Q.10      800       400       160         64       32        16 
a).400
b). 32
c).64
d).16
e) none of these

Directions: (Q 11 – Q 15). What should come in place of question mark (?) in the following series. 
Q.11        13       22          57          212           1035          ? 
a). 4170
b). 5075
c). 6174
d).6205
e) None of these.

Q.12.      5         6         14        41        105         ? 
a).215
b). 315
c).230
d) 340
e) None of these.

Q.13.   123       173        231      297       371        453        ? 
a).540 
b). 543 
c).580 
d). 510 
e). None of these

Q.14.    9         18       ?            92       173         294 
a). 32 
b). 43 
c). 27 
d). 18 
e) None of these

Q.15.     1378      687       340.5        ?         78.125           30.0625 
a).166.25 
b). 186.25 
c). 178.25 
d). can’t be determined 
e) None of these 
Solution

Ans.1 –d. 
2nd term = (1st term * 1.5 + 0.5) 
3rd term =(2nd term * 2 + 1) 
4th term = (3rd term * 2.5 + 1.5) and so on. 

Ans.2 – d 
2nd term = (1st term + 13) 
3rd term = (2nd term + 23) 
4th term = (3rd term + 33) 
5th term = ( 4th term + 43) and so on, 
Hence 117 is wrong. 

Ans.3 – a 
2nd term = (1st term * 2 – 22) 
3rd term =(2nd term * 4 – 42) 
4th term = (3rd term * 8 – 82) 
5th term = (4th term * 16 – 256) 
6th term = (5th term * 32 – 1024) 
Hence 28 is wrong. 

Ans.4 –b 
44 /2= 22 
22 * 3 =66 
66/2=33 
33*3=99 
99/2=44.5 
44.5*3=133.5 

Ans.5 – d 
The series is *2 + 3, *2 + 3, .... 
Hence 14 is wrong ans. 

Ans.6 – c 
1st term + 13 – 1 = 7 
7 + 23 -2=13 
13 + 33 -3=37 
37 + 43-4=97 
97 + 53-5=217 

Ans.7 – b 
The series goes as follows 
2 * 1 + 7 * 1 =9 
9 * 2 + 6 * 2=30 
30 * 3 + 5 * 3 = 105 
105 * 4 + 4 * 4=436 
436 * 5+ 3 * 5=2195 
2195 * 6 + 2 * 6=13182 

Ans.8 – d 
The series is x2 + 1, x3 -2, x4 + 3,.... 

Ans.9 – a). 
The series is x0.5, x1.5, x 2.5, x3.5, .... 

Ans.10 – c. 
800/2=400 
400* 2/5=160 
160/2=80 
80*2/5=32 
32/2=16 

Ans.11 –d. 
1st term * 2 – 22 
2nd term * 3 - 32 
3rd term * 4 - 42 
4th term * 5 - 52 
And so on. 

Ans.12 –d 
02 + 5 = 5 
12 + 5= 6 
32 + 5= 14 
62 + 5 = 11 
102 + 5=105 
152+ 5=230 

Ans.13 –b 
123 + 50=173 
173+58=231 
231+66=297 
297+74=371 
371+82=453 
453+90=543 

Ans.14 –b. 
2nd term = 1st term + 12 
3rd term = 2nd term + 33 
4th term = 3rd term + 52 
5th term = 4th term + 72 and so on. 

Ans. 15 – a. 
2nd term = 1378/2 – 2=687 
3rd term = 687/2 -3=340.5 
4th term = 340.5/2 – 4=166.25 
5th term = 166.25/2 -5=78.125 
6th term = 78.125/2 -6=30.0625
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