Question

A progression has a first term of 12 and a fifth term of 18.

Find the sum of the first 25 terms in the progression is aritmetic.

Answer 1

Is the difference 1.5?

Answer 2

+d +d +d +d
12 -->a2 ---> a3 --->a4 --->18
therefore, 12+4d = 18, d= (18-12)/4 = 1.5

Answer 3

Ok, so what's the sum?

Answer 4

T(25) = a +(n-1)(1.5) = 12+(25-1)(1.5) = 48
Sum = (12+48)*25/2 = 1500/2 =750

Answer 5

Thank you :)

Answer 6

you're welcome. I don't know if i get it correct :S

Answer 7

I tried and got the same answer. Can you see the most recent post I posted?