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Question
Q. First term is of arithmatic progression sequence is 28 and the difference between consecutive numbers is 8 , Find the sum numbers 10th, 11th, 12th, 13th and 14th terms.
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Step : 1
Sum of 10 position is (10/2)[2*28 + (10 - 1)x 8 ]
= (5)[56 + (9)x 8 ]
= (5)[56 + 72 ]
= (5)[128]
ie. S10 = (640)
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Step : 2
Sum of 11 position is (11/2)[2*28 + (11 - 1)x 8 ]
= (5.5)[56 + (10)x 8 ]
= (5.5)[56 + 80 ]
= (5.5)[136]
ie. S11 = (748)
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Step : 3
Sum of 12 position is (12/2)[2*28 + (12 - 1)x 8 ]
= (6)[56 + (11)x 8 ]
= (6)[56 + 88 ]
= (6)[144]
ie. S12 = (864)
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Step : 4
Sum of 13 position is (13/2)[2*28 + (13 - 1)x 8 ]
= (6.5)[56 + (12)x 8 ]
= (6.5)[56 + 96 ]
= (6.5)[152]
ie. S13 = (988)
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Step : 5
Sum of 14 position is (14/2)[2*28 + (14 - 1)x 8 ]
= (7)[56 + (13)x 8 ]
= (7)[56 + 104 ]
= (7)[160]
ie. S14 = (1120)
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Step : 6
so the sequance of the sum numbers from position are.
S10 = 640
S11 = 748
S12 = 864
S13 = 988
S14 = 1120
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