Question Details

Given below are two number series. Series I is a missing series while series II is a wrong number series which follows pattern of series I only.

1. 11, P, 181, 350, 639, 1000
2. 242, 251, 255, 280, 329, 450, 619

If ‘y’ is the wrong number of the series II, then find the value of ‘2y+1’.

Options

A

493

B

561

C

503

D

511

E

901

Show Answer

Correct Answer :

Option C

503

Solution :

The correct option is 503.

Let us analyze the pattern of Series I to find the logic:

Series I: 11, P, 181, 350, 639, 1000

Let us calculate the differences between the consecutive known terms of Series I:
1000-639=361=192
639-350=289=172
350-181=169=132

The differences are the squares of consecutive prime numbers: 13, 17, and 19. Continuing this pattern backwards, the differences before 132 should be the squares of the prime numbers 11 and 7:
181-P=112=121P=181-121=60
P-11=72=4960-11=49 (which is correct)

Thus, the logic of the series is adding the squares of consecutive prime numbers.

Now, let us examine Series II, which follows the same logic (adding squares of consecutive prime numbers):

Series II: 242, 251, 255, 280, 329, 450, 619

Let us check the differences between the terms from right to left:
619-450=169=132
450-329=121=112
329-280=49=72
280-255=25=52

The consecutive prime numbers in descending order starting from 13 are: 13, 11, 7, 5, 3, and 2. Therefore, the next differences going backwards should be:
32=9
22=4

Let us apply these differences to find the correct terms starting from 255:
The term before 255 should be: 255-32=255-9=246
The term before 246 should be: 246-22=246-4=242 (which matches the first term)

In Series II, the term given is 251 instead of 246. Therefore, the wrong number in Series II is:
y=251

We need to find the value of 2y+1:
2y+1=2(251)+1=502+1=503

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