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NCERT Class XI Mathematics - Sequences and Series - Solutions
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Question : 80 of 106
Marks:
+1,
-0
If the sum of three numbers in A.P., is 24 and their product is 440, find the numbers.
Solution:
Let the three numbers in A.P. be a – d, a, a + d. Then (a – d) + a + (a + d) = 24 ⇒ 3a = 24 ⇒ a = 8 .....(i) and (a – d) a (a + d) = 440 ⇒ a = 440 ⇒ 8 = 440 [from (i)] ⇒ 64 – = 55 ⇒ = 64 – 55 ⇒ = 9 ⇒ d = ±3 Case (i) : If d = 3, then the numbers are 8 – 3, 8, 8 + 3 i.e., 5, 8, 11 Case (ii) : If d = – 3, then the numbers are 8 – ( – 3), 8, 8 + (– 3) i.e., 11, 8, 5
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