The sum of the 16th term of an AP is 240 and the sum of the next 4 term is 220. Find the first term and the come difference
sum(16) = 8(2a + 15d) = 240
2a + 15d = 30
sum(20) = 10(2a + 19d) = 240+220 = 460
2a + 19d = 46
subtract:
4d = 16
d = 4
back in 2a + 15d = 30
2a +60 = 30
a = -15