In an AP if a = 1, an = 20 and Sn = 399, then n is
A. 19
B. 21
C. 38
D. 42
Answer:C
In an AP if a = 1, an = 20 and Sn = 399, then n is
A. 19 B. 21 C. 38 D. 42
Explanation: 15. If the numbers n – 2, 4n – 1 and 5n +2 are in AP, then the value of n is: