The lengths

The lengths of the twelve poles form an Arithmetic Progression (A. P). If the third pole is 3m and the eighth pole is 5 m, find the
(i) Length of the first pole
(ii) Sum of the length of the poles

Correct answer:

a1 =  2.2 m
s =  52.8 m

Step-by-step explanation:

AP n=12 a3=3 m a8=5 m  a3=a1+2 d a8=a1+7 d 3=a1+2 d 5=a1+7 d  a1+2d=3 a1+7d=5  Row2Row1Row2 a1+2d=3 5d=2  d=52=0.4 a1=32d=32 0.4=2.2=511 m=2.2 m  a1=511=2.2 d=52=0.4
a12=a1+11 d=2.2+11 0.4=533=6.6 m  s=2a1+a12 n=22.2+6.6 12=5264 m=52.8 m

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