# 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 8^{th} set of letter is mailed

**Solution:**

The number of letters mailed forms a G.P: 4, 4^{2}, .... , 4^{8}

Here, a = 4, r = 4, n = 8

Using the sum of a G.P. formula,

S_{n} = a (r^{n} - 1)/(r - 1)

S_{8} = 4 (4^{8} - 1)/(4 - 1)

= 4(65536 - 1)/3

= 4 x 65535/3

= 4 x 21845

= 87380

It is given that the cost to mail one letter is 50 paisa.

Therefore, cost in ₹ for mailing 87380 letters = 50/100 x 87380 = 43690

Thus, ₹ 43690 spent when on the postage when 8^{th} set of letter is mailed

NCERT Solutions Class 11 Maths Chapter 9 Exercise ME Question 29

## 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 8^{th} set of letter is mailed.

**Summary:**

We assumed that the chain is not broken and considering that it costs 50 paise to mail one letter, the amount spent on the postage when the 8^{th} aet of letter is mailed would be ₹ 43690