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  • 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 o

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 8th set of letter is mailed.

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best_answer

The numbers of letters mailed forms a GP : 4,4^2,4^3,.............4^8

first term  = a=4

common ratio=r=4

number of terms = 8

We know that the sum of GP is 

                                    S_n=\frac{a(r^n-1)}{r-1}

                                             =\frac{4(4^8-1)}{4-1}

                                            =\frac{4(65536-1)}{3}

                                            =\frac{4(65535)}{3}

                                          =87380

costs to mail one letter are 50 paise.

Cost of mailing 87380 letters

                                               =Rs. \, 87380\times \frac{50}{100}

                                                 =Rs. \,43690

Thus, the amount spent when the 8th set of the letter is mailed is Rs. 43690.

Posted by

seema garhwal

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