Problem Solving (PS) | Re: The sum of the fourth and twelfth term of an arithmetic

Term = T
Common difference = D

T4+T12=20
T4=T1+3D
T12= T1+11D

2T1+14D=20 (1)

Sum of first 15 terms = 15*(T1+T15)/2
T15=T1+14D

Sum of first 15 terms = 15*(2T1+14D)/2 (2)

(1) & (2)
Answer is 150

Statistics : Posted by Abolnasr • on 06 Aug 2009, 23:05 • Replies 12 • Views 69626

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