Find S25 for 4 + 14 + 24 + 34 +…
A.3090

B.3100

C.3110

D.3120

Question

Find S25 for 4 + 14 + 24 + 34 +…
A.3090
	
B.3100
	
C.3110
	
D.3120

lncognlto · Answer

As this is an arithmetic series, the formula for the sum of n terms, which we shall call Sn, is$$Sn = \frac{ n }{ 2 }(2a + (n - 1)d)$$where a is the first term of the sequence, and d is the difference between terms.

anonymous · Answer

the options seem to be wrong ^^

lncognlto · Answer

n in this case is given to be 25, from S25, while a is 4, as that is the first term of this series, and d is equal to the difference between two terms, which remains constant over the series, so in this case 14 - 4 = 10 = d.

lncognlto · Answer

Nah, I get an answer within the options given. @aajugdar

lncognlto · Answer

Now we plug these values into the formula and calculate!

anonymous · Answer

my bad
i calculated 25th term

lncognlto · Answer

xD
@WAyne5 does this make sense so far? What answer do you get?