The a.p. in which 4th term is -15 and 9th term is -30. Find the sum of the first 10 numbers.
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according to the question,
a + 3d = -15
a + 8d = -30
=> 5d = -15
=> d = -3
a= -15 -3d = -15 -3(-3) = -15 +9 = -6
therefore S10 = 10/2 [ 2×(-6) + 9(-3)]
= 5 (-12-15)
=5(-27) = -135(ans)
Hope it helps
a + 3d = -15
a + 8d = -30
=> 5d = -15
=> d = -3
a= -15 -3d = -15 -3(-3) = -15 +9 = -6
therefore S10 = 10/2 [ 2×(-6) + 9(-3)]
= 5 (-12-15)
=5(-27) = -135(ans)
Hope it helps
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