Question

the 9th and 19th terms of a series in a.p are respectively 35 and 75 .find the series and its 20th term.

Answer 1

an=a+(n-1)d
a9=a+(9-1)d
35=a+8d
a=35+8d take it as 1

a19=a+18d
75=a+18d take it as 2

put 1 in 2
75=35+8d+18d
40=26d
d=20/13

put d= 4 in 1
a=35+8*20/13
a=35+160/13
a=(455+160)/13
a=615/13

a20=a+19d
=>615/13+380/13
=>995/13

Answer 2

This is your answer
I hope it help you