an AP consists of 13 terms the sum of the three middle most terms is 135 and the sum of the last three terms is 240 find the AP
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Step-by-step explanation:
n = 13
Sum of middle three terms = 135
A(6) + A(7) + A(8) = 135
a+5d + a+6d + a+7d = 135
3a + 18d = 135
a + 6d = 45 -------(1)
A(11) + A(12) + A(13) = 240
a+10d + a+11d + a+12d = 240
3a + 33d = 240
a + 11d = 80 -----(2)
from equation (2) - (1)
5d = 35
d = 7
a = 45 - 6(7) = 45 - 42 = 3
A.P. is -
3 , 10 , 17 , 24 , 31 ,..............,87
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