Forty - one forks are so arranged that each products ` 5 beat//s` when sounded with its near fork . If the frequency of last fork is double the frequency of first and last fork , respectively are

Options

A. `200,400`
B. `205,410`
C. `195,390`
D. `100,200`

Answer

A

Explanation

Let the frequency of first tuning fork ` = n` and that of last `= 2n`
` n , n + 5 , n + 10, n + 15 , … 2n` this forms `AP`
Formula of `AP l = a + (N - 1) r` where l = Last term , a = First term , N = Number of term , r = Common difference
` 2 n = n + ( 41 - 1) 5`
` 2 n = n + 200`
`n = 200 and 2n = 400`