A person writes a letter to four of his friends. He asks each one of them to copy the letter 'and mail to four different persóns with instruction that they move the chain similarly. Assuming that the chain is not broken and that it costs 50 paise to mail one letter. Find the amount spent on the postage when `8^ th ` set of letter is mailed.

Explanation

Here `a=4, r=4`

Total number of letters in all 8 sets `=4(4^8-1)/4-1=4(4^8-1)/3`

Amount spent on the postage when `8^ th ` set of letter is mailed `=4 xx 65535 xx 0.50/3, doteq` Rs. 43690