Find the value of a 25 - a 15 for the A.P: 6,9,12,15,...........

This question is similar to Question 8 or 2nd CBSE Class 10 Sample Paper 2019 Boards

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Question 1 – Choice 1 Find the value of a25 − a15 for the AP: 6, 9, 12, 15, ……… Given A.P. 6, 9, 12, 15, ……… Thus, a = 6 & d = 9 − 6 = 3 We know that an = a + (n – 1) d Finding a25 and a15 Finding a25 a25 = a + (25 – 1) d a25 = a + 24d Putting a = 6, d = 3 a25 = 6 + 24 × 3 a25 = 6 + 72 a25 = 78 Finding a15 a15 = a + (15 – 1) d a15 = a + 14d Putting a = 6, d = 3 a25 = 6 + 14 × 3 a25 = 6 + 42 a25 = 48 Thus, a25 − a15 = 78 − 48 = 30

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.