Directions (1 - 3): Complete the following series.
1.
2, 4, 12, 4, 240, ?
a) 960
b) 1440
c) 1080
d) 1920
e) None of these
2.
2, 5, 9, 19, 37, ?
a) 76
b) 74
c) 75
d) 73
e) None of these
3.
4, -8, 16, -32, 64, ?
a) 128
b) -128
c) 192
d) -192
e) None of these
Directions (4 - 5): Find the wrong term in the following given series.
4.
2, 9, 28, 65, 126, 216, 344
a) 2
b) 28
c) 65
d) 126
e) 216
5.
10, 26, 74, 218, 654, 1946, 5834
a) 26
b) 74
c) 218
d) 654
e) 1946
Answers:
1. a)
2, 4, 12, 48, 240, ….
The pattern is: to arrive at a term, the previous term is being multiplied by (n+1) where ‘n’ keeps on increasing by 1 for every term.
2
4
= 2 × (2 + 0)
12
= 4 × (2 + 1)
48
= 12 × (2 + 2)
240
= 48 × (2 + 3)
⇒ Next term = 240 × (2 + 4) = 240 × 6 = 1440
2. c)
2, 5, 9, 19, 37, …..
The pattern is: every number is arrived at previous number multiplied by 2 and then alternate addition and subtraction by 1 i.e.
2
5=2×2+1
9=5×2-1
19=9×2+1
37=19×2-1
the next term 37×2+1 = 75
3. b)
4, -8, 16, -32, 64, ….
The pattern is: Every number is arrived at by multiplying previous alternate number with ‘4’ as shown below:
4*4 = 16
-8*4 = -32
16*4 = 64
-32*4 = -128
Hence, ‘-128’ is the correct answer.
4. e)
2, 9, 28, 65, 126, 216, 344.
The pattern in the series is that the series is triangular as shown below:
In the triangular series, the difference between consecutive terms is written below the numbers and then, difference between consecutive differences is
written below & this process carries on until all the difference become equal. In the figure above there was an error & we have corrected it.
5. d)
10, 26, 74, 218, 654, 1946, 5834
The pattern is: to arrive at next term, the previous is multiplied by 3 and subtracted by 4:
10
10
× 3 – 4 = 26
26
× 3 – 4 = 74
74
× 3 – 4 = 218
218
× 3 – 4 = 650 ≠ 654
650
× 3 – 4 = 1946
1946
× 3 – 4 = 5834
Here, ‘654’ was wrong.
Thanks.
