arithmatic progression

Q) The sum of first 15 terms of an A.P. is 750 and its first term is 15. Find its 20th term. Ans: Given that a = 15 and Sum of 15 terms of an A.P.  S15 = 750 We know that sum of n terms of an A.P.  Sn = (2a + (n-1) d) […]

Q) Which term of the A.P. : 65, 61, 57, 53,………… is the first negative term. Ans: This is A.P. of decreasing order. In the given A.P., we can see that: First term a = 65 and common difference d = -4 Let first negative term be nth term, say Tn We know that nth

Q) How many terms are there in an A.P. whose first and fifth terms are -14 and 2, respectively and the last term is 62. Ans: Let’s consider an A.P with first term as N1 and common difference as ‘d’. Next, we know that nth term of an A.P.  =  a + (n-1) d  

Q) Prerna saves Rs. 32 during the first, month, Rs. 36 in the second month and Rs. 40 in the third month. if she continues to save in this manner, in how many months will she save Rs. 2,000? Ans: From the given data, we get AP as, 32, 36, 40, ….. Let’s consider that

Q)  Solve the equation for x: 1 + 4 + 7 + 10 + …. + x = 287 Ans:  We can see that it is AP with first term a = 1 and common difference d = 3 Let x be the value of nth term and we need to find value of this

Q) How many terms of the arithmetic progression 45, 39, 33, …….. must be taken so that their sum is 180? Explain the double answer. Ans: In AP of 45,39, 33, ……. a = 45, d = – 6, Sum of n terms of AP, Sn = (2a + (n-1)d) 180 = (2 x 45

Q) 250 logs are stacked in the following manner: 22 logs in the bottom row, 21 in the next row, 20 in the row next to it and so on (as shown by an example). In how many rows, are the 250 logs placed and how many logs are there in the top row? Ans:  VIDEO

Q) The ratio of the 11th term to 17th term of an A.P. is 3:4. Find the ratio of 5th term to 21st term of the same A.P. Also, find the ratio of the sum of first 5 terms to that of first 21 terms. Ans: VIDEO SOLUTION STEP BY STEP SOLUTION We know that nth term