An arithmetic progression has 10 terms. Sum of the 10 terms is 220. Sum of the odd terms is 100. Find the first term and common difference.

Answer 1

10/2 (2a+9d) = 220

Now, the odd terms are
a, a+2d, a+4d, ...
So they form a 5-term AP whose common difference is 2d, and whose sum is

5/2 (2a+4(2d)) = 100

Now you can find a and d.