Reasoning : Logical Reasoning & Analytical Ability

Q 115 / 325

UPSC CSE Prelims 2020

‘A’ is sixteenth from the left end in a row of boys and ‘V’ is eighteenth from the right end. ‘G’ is eleventh from ‘A’ towards the right and third from ‘V’ towards the right end. How many boys are there in the row?

EXPLANATION

Correct Option (2)

The total number of boys in the row can be determined by establishing the position of a common individual from both ends of the row.

  • 'A' is sixteenth from the left end. This implies there are 15 boys to the left of 'A'.
  • 'G' is eleventh from 'A' towards the right. This means there are 10 boys positioned between 'A' and 'G'. Consequently, 'G' is at the (16 + 11) = 27th position from the left end.
  • 'V' is eighteenth from the right end.
  • 'G' is third from 'V' towards the right end. This indicates that 'G' is three positions closer to the right end than 'V'. Therefore, 'G' is at the (18 - 3) = 15th position from the right end.

Using 'G's position from both ends, the total number of boys in the row is calculated as:

Total boys = (Position of 'G' from left) + (Position of 'G' from right) - 1

Total boys = 27 + 15 - 1 = 42 - 1 = 41.

Alternatively, by summing the segments:

  • Boys to the left of 'A' = 15
  • 'A' = 1
  • Boys between 'A' and 'G' = 10
  • 'G' = 1
  • Boys to the right of 'G' = 14 (since 'G' is 15th from the right end, there are 14 boys to its right)

Total boys = 15 + 1 + 10 + 1 + 14 = 41.

Incorrect Options:

The problem provides sufficient data to precisely determine the number of boys in the row. Options 1 (40) and 3 (42) would result from miscalculations, such as errors in determining relative positions or incorrect application of the formula for total individuals in a linear arrangement. Option 4 ('Cannot be determined due to insufficient data') is incorrect as the given information allows for a definitive calculation of the total number of boys.