Question 38

Which number will replace the question mark (?) in the following series?
15, 32, 55, ?, 127, 180

Solution

Let's assume assume 'y' in place of question mark.

Here the double difference is applicable.

So (y-55)-23 = 8

y-78 = 8

y = 78+8 = 86

simiallry (127-y)-(y-55) = 10

182-2y = 10

2y = 182-10 = 172

y = 86

simiallry (127-y)-53 = 12

74-y = 12

y = 74+12

y = 86

Hence 86 will come in place of the question mark.

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