How many terms of the Arithematic sequence 60,56,52,48..... add up to 368?
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S n = 368
60,56,52,48,.......
a = 60 d = 56 - 60 = -6
(n/2) [ 2a + (n-1) d ] = 368
(n/2) [ 2(60) + (n-1)(-4) ] = 368
(n/2) [ 120 - 4 n + 4 ] = 368
(n/2) [ 124 - 4 n ] = 368
n [ 124 - 4 n ] = 368 x 2
n [ 124 - 4 n ] = 368 x 2
124 n - 4 n² = 736
4 n² - 124 n + 736 = 0
÷ by 4 = > n² - 31 n + 184 = 0
(n-23) (n-8) = 0
n = 23,8
Sum of 8 or 23 terms of arithmetic sequence is 368.
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