NCERT Class XI Mathematics - Sequences and Series - Solutions

Question : 107

Total: 106

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 persons 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 8th set of letter is mailed.

Solution:

Number of letters posted in 1st set, 2nd set, 3rd set ..... are 4,42,43, ...... Total letters posted upto 8th set are
4 + 42 + .... to 8th term. Since, this forms a G.P.
∴ S8 =

4(48−1)

4−1

(65536 - 1) =

(65535)
= 4 × 21845 = 87380
Hence the amount spent on the postage
= Rs. (0.50 × 87380) [Since 50 paise = Rs. 0.50]
= Rs. 43690.

Go to Question:

Prev Question

Next Question