Question

Identify wrong number in the series.
5, 8, 20, 42, 124, 246, 736
(a) 8
(b) 20
(c) 42
(d) 124​

Answer 1

Answer:

(B)-20

Step-by-step explanation:

2nd term = (1st term x 2 - 2) = (5 x 2 - 2) = 8.;

3rd term = (2nd term x 3 - 2) =( 8 x 3 - 2) = 22;

4th term = (3rd term x 2 - 2) = (22 x 2 - 2) = 42;

5th term = (4th term x 3 - 2) = (42 x 3 - 2) = 124 and so on

∴ 20 is wrong.

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Answer 2

Given:

A series of numbers 5, 8, 20, 42, 124, 246, 736

To Find:

The wrong number in the series is?

Solution:

The given problem can be solved by developing a common logic between every term.

1. The given series is 5, 8, 20, 42, 124, 246, 736

2. The second term in the series is obtained as,

=> Second term = (first term x 2) - 2 = 10 - 2 = 8. ( Correct term )

3. The third term of the series is obtained as,

=>Third term = (Second term x 3) - 2 = 24 - 2 = 22. ( Incorrect term )

4. The fourth term of the series is obtained as,

=>Fourth term = (Third term x 2) - 2 = 44 - 2 = 42. ( Correct term )

5. The fifth term of the series is obtained as,

=>Fifth term = (Fourth term x 3) - 2 = 126 - 2 = 124. ( Correct term )

6. The sixth term of the series is obtained as,

=>Sixth term = (Fifth term x 2) - 2 = 248 - 2 = 246. ( Correct term )

7. The seventh term of the series is obtained as,

=>Seventh term = (Sixth term x 3) - 2 = 738 - 2 = 736. ( Correct term )

Therefore, the wrong number in the series is 20. Option B is the correct answer.