SOLUTION: Twelve iron poles are used for pillar and the lengths of the poles form an arithmetic progression.If the third pole is 4mand seventh is 10m,find the length of the poles in order of

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Question 1158039: Twelve iron poles are used for pillar and the lengths of the poles form an arithmetic progression.If the third pole is 4mand seventh is 10m,find the length of the poles in order of A.P and the cost of all poles if a meter is 45.00Naira
Answer by Boreal(15235) About Me  (Show Source):
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a3=4
a7=10
sum is (n/2)(a1+an)
a3=a1+2d
a7=a1+6d
so 4=a1+2d and 10=at+6d
4d=6
d=1.5 m
a12=a7+5d=10+7.5=17.5 m
a3=4=a1+2d
so a1=1
a12=17.5
sum is 6(18.5)=111 m
cost is 111*45=4995 Naira
posts are
1, 2.5, 4, 5.5, 7, 8.5, 10, 11,5, 13, 14,5, 16, 17,5