A sequence is given by (2frac{1}{2}, 5, 7frac{1}{2}, …..) if the nth term is 25, find n
-
A.
9 -
B.
10 -
C.
12 -
D.
15
Correct Answer: Option B
Explanation
(a = 2frac{1}{2}, nth = a + (n-1)d Rightarrow 25 = 2frac{1}{2} + (n-1)2frac{1}{2}\
25 = frac{5}{2}+(n-1)frac{5}{2} Rightarrow 22frac{1}{2} = frac{5n-5}{2}Rightarrow frac{45}{2} = frac{5n-5}{2}\
45 = 5n – 5 Rightarrow 5n = 50 Rightarrow n = 10)