Question Details

What number would replace question mark (?) in the series given below?

3, 8, 17, 32, 57, ?, 177

Options

A

100

B

89

C

95

D

106

Correct Answer :

100

Solution :

The correct option is 100.

To find the number that replaces the question mark (?), let us analyze the differences between consecutive terms in the given series:

The given series is: 3, 8, 17, 32, 57, ?, 177

Let's find the difference between consecutive terms:
First difference:
8-3=5
Second difference:
17-8=9
Third difference:
32-17=15
Fourth difference:
57-32=25

Now, let us examine the sequence of these differences: 5, 9, 15, 25.
We can find the differences between these differences (the second-level differences):
Difference between 9 and 5:
9-5=4
Difference between 15 and 9:
15-9=6
Difference between 25 and 15:
25-15=10

The second-level differences are: 4, 6, 10.
Looking at this second-level difference pattern, we can see a relationship of multiplying by 2 and then subtracting a value, or adding consecutive even numbers with an increasing gap:
Let's find the differences of the second-level differences (third-level differences):
6-4=2
10-6=4
The differences of the second-level differences are 2, 4, which suggests the next third-level difference should be 8 (doubling the previous difference) or 6 (increasing by 2).
Let's test the doubling pattern for third-level differences: 2, 4, 8, 16...
If the next third-level difference is 8:
The next second-level difference would be:
10+8=18
The next first-level difference would be:
25+18=43
The missing term (?) would then be:
57+43=100

Let us verify if this rule holds for the final term (177):
The next third-level difference would be:
8×2=16
The next second-level difference would be:
18+16=34
The next first-level difference would be:
43+34=77
The next term after 100 would be:
100+77=177
Since this matches the last term in the given series, the pattern is verified and correct.

Therefore, the number that replaces the question mark is 100.

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