Question

in an arithmetic sequence the 5th term is 20 and 10th term is 40.what is the 15 th term? what is the 1st term?​

Answer 1

Answer:

$5th \: term = 20 \\ a + 4d = 20 \\ 10th \: term = 40 \\ a + 9d = 40 \\ subtracting \: both \: the \: terms \\ a + 9d - a - 4d = 40 - 20 \\ 5d = 20 \\ d = 4 \\ now \\ a + 4d = 20 \\ a + 4 \times 4 = 20 \\ a + 16 = 20 \\ a = 4 \\ 15th \: term = a + 14d \\ = 4 + 4 \times 14 \\ = 4 + 56 \\ = 60$

Answer 2

1st term is 4 & 15th term is 60 ....