Question Details

Find out the missing term of the number series given below.

60, ?, 63.6, 70.8, 99.6, 243.6

Options

A

67.4

B

61.2

C

59.6

D

57.8

E

63.2

Show Answer

Correct Answer :

Option B

61.2

Solution :

To find the missing term in the given series, let us first examine the differences between the consecutive known terms of the series:

60, ?, 63.6, 70.8, 99.6, 243.6

Let the terms be denoted as T1, T2, T3, T4, T5, and T6.

Let us calculate the differences between the latter terms:

Difference between the 4th and 3rd terms:
T4-T3=70.8-63.6=7.2

Difference between the 5th and 4th terms:
T5-T4=99.6-70.8=28.8

Difference between the 6th and 5th terms:
T6-T5=243.6-99.6=144.0

Now, let us analyze the pattern in these differences (7.2, 28.8, 144.0):

28.87.2=4
144.028.8=5

The ratio between consecutive differences is increasing by 1 each time. Following this logical pattern, the ratio of the difference before 7.2 should be 3, and the one before that should be 2.

Let us denote the difference between the terms as dn=Tn+1-Tn. The differences are:

d4=28.8
d3=7.2 (since d4=d3×4)
d2=7.23=2.4
d1=2.42=1.2

Alternatively, we can express the difference dn as:
dn=1.2×n!

Using this pattern to find the missing term T2:

T2=T1+d1=60+1.2=61.2

Let us verify with the next term:

T3=T2+d2=61.2+2.4=63.6

Since this perfectly matches the third term in the series, the missing term is 61.2.

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