In a row of boys P is 16th from the left. There are thrice as many boys behind him as in front. What is the number of boys sitting between P and the one who is 8th from the right?

37

As there are 15 boys in front of P therefore 45 boys are behind of him.

Total number of boys in the row: T = 16 + 45 => 61

Now required answer is: T = L + R + B/W = 61

                                     16 + 8 + B/W  = 61

                                       24 + B/W = 61

                                              B/W = 37