NCERT Class 11 Mathematics Solutions: Chapter 9 –Sequences and Series Miscellaneous Exercise 9 Part 16

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Sum of a Geometric Series

Sum of a Geometric Series

Sum of a Geometric Series

1. 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 paise to mail one letter. Find the amount spent on the postage when set of letter is mailed.

Answer:

The numbers of letters mailed forms a G.P.:

First term

Common ratio

Number of terms

It is known that the sum of n terms of a G.P. is given by

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

Cost of mailing 87380 letters

So, the amount spent when set of letter is mailed is .

2. A man deposited in a bank at the rate of simple interest annually. Find the amount in year since he deposited the amount and also calculate the total amount after years.

Answer:

It is given that the man deposited in a bank at the rate of simple interest annually.

Interest in first year

Amount in year

Amount after years