<PRE><B>Question 838572</B>
The first term of an AP is 6 and the fifth term is 12. The progression has n terms and the sum of all the terms is 90. 

What is the value of n? (how many terms)

Tn = a+(n-1)d

a=6 , 
T5 = 12

12=6+(5-1)d

12=6+4d

12-6=4d
6=4d
d=3/2

Tn = 90

90=6+(n-1)*1.5

90-6= 1.5n -1.5

84+1.5=1.5n

85.5/1.5 = n

57 = n

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