Question

kumar writes a letter to four of his friends.he asks each one of them to copy the letter and mail to four different person with the instruction that they continue the process similarly.assuming that the process is unaltered and it costs ₹3 to mail one letter find the amount spent on postage when 12th set of letters is mailed.
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Answer 1

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Answer:

Rs 262140

Step-by-step explanation:

Kumar 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 the instruction that they continue the process similarly. Assuming that the process is unaltered and it costs Rs. 3 to mail one letter, find the amount spent on postage when 8th set of letters is mailed. ​

4   , 4 *4 = 16    16*4 = 64   and so on

This is a GP

where a = 4  r = 4

8th Set = ar⁷ = 4 * 4⁷ = 4⁸ = 65536

Cost = 2 * 65536 = 131072  Rs

To find total Cost Till 8th set

Total Letters mailed

= a(r⁸ - 1)/(r-1)

= 4(4⁸-1)/(4-1)

= 4(65536 - 1)/3

= 87380

Cost = 3 * 87380 = 262140 Rs