The sum of the first six terms oa an AP is 42.the ratio fo the 10th term to 30th term of an ap is 1/3.calculate the first term and the 13th term.
Let a be the first term and d be the common difference
Sum of 6 terms = S6 = (6/2) [ 2a + 5d ] = 42 or 2a+5d = 14 …(1)
from eqn.(1), if we substitute a = d, then we get a = 2
13th term = 2+12(2) = 26