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Class XI Chapter 9 – Sequences and Series Maths ______________________________________________________________________________ Thus, total interest to be paid = 10% of 18000 + 10% of 17000 + 10% of 16000 + ….. + 10% of 1000 = 10% of (18000 + 17000 + 16000 + ….. + 1000) = 10% of (1000 + 2000 + 3000 + ….. + 18000) Here, 1000, 2000, 3000 …. 18000 forms an A.P. with first term and common difference both equal to 1000. Let the number of terms be n . n 18000 1000 1 1000 n 18 18 1000 2000 .... 18000 2 1000 18 1 1000 2 9 2000 17000 171000 Total interest paid = 10% of (18000 + 17000 + 16000 + …. + 1000) = 10% of Rs.171000 = Rs. 17100 Cost of scooter = Rs. 22000 + Rs. 17100 = Rs. 39100. 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. Solution 29: The numbers of letters mailed forms a G.P. : First term = 4 Common ratio = 4 Number of terms = 8 It is known that the sum of n terms of a G.P. is given by S n n a r 1 r 1 8 2 8 4,4 ,....4 4 4 1 4 65536 1 4 65535 S8 421845 87380 4 1 3 3 It is given that the cost to mail one letter is 50 paisa. Cost of mailing 87380 letters 50 = Rs.87380 Rs.43690 100 Thus, the amount spent when 8 th set of letter is mailed is Rs. 43690. Printed from Vedantu.com. Register now to book a Free LIVE Online trial session with a Top tutor.
Class XI Chapter 9 – Sequences and Series Maths ______________________________________________________________________________ Question 30: A man deposited Rs. 10000 in a bank at the rate of 5% simple interest annually. Find the amount in 15 th year since he deposited the amount and also calculate the total amount after 20 years. Solution 30: It is given that the man deposited Rs. 10000 in a bank at the rate of 5% simple interest annually. 5 Rs.10000 Rs.500 100 Interest in first year Amount in 15 th year Rs.10000 14 Rs.500 Rs.10000 Rs.7000 Rs.17000 Amount after 20 years Rs.10000 20 Rs.500 Rs.10000 Rs.10000 Rs.20000 . 10000 500 500 .... 500 14 times Rs.10000 500 500 .... 500 20times Question 31: A manufacturer reckons that the value of a machine, which costs him Rs. 15625, will depreciate each year by 20%. Find the estimated value at the end of 5 years. Solution 31: Cost of machine = Rs. 15625 Machine depreciates by 20% every year. Therefore, its value after every year is 80% of the original cost i.e., Value at the end of 5 years 4 4 4 15625 .... 51024 5120 5 5 5 5 times Thus, the value of the machine at the end of 5 years is Rs. 5120. 4 5 of the original cost. Printed from Vedantu.com. Register now to book a Free LIVE Online trial session with a Top tutor.
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Class XI Chapter 1 - Sets Maths ___
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Class XI Chapter 2 - Relations and
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Class XI Chapter 3 - Trigonometric
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Class XI Chapter 4 - Principle of M
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Class XI Chapter 5 - Complex Number
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Class XI Chapter 6 - Linear Inequal
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Class XI Chapter 7 - Permutation an
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Class XI Chapter 8 - Binomial Theor
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Class XI Chapter 9 - Sequences and
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Class XI Chapter 10 - Straight Line
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Class XI Chapter 11 - Conic Section
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Class XI Chapter 12 - Introduction
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Class XI Chapter 13 - Limits and De
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Class XI Chapter 14 - Mathematical
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Class XI Chapter 15 - Statistics Ma
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