An AP has 40 terms. Its 40th term is 122 and its common difference is 3. Find its 33rd term.

Going back from the 40th term to the 33rd term is 7 steps, so $a_{33}=a_{40}-7d=122-21=101$. Adding instead of subtracting gives 143; using 8 steps gives 98 and using 6 steps gives 104.