In a mobile plan, the fee in the first month is (₹900) and the discount increases by (₹35) each month. What is the fee in the (10)th month?

Correct answer: ₹585

Since the discount rises by ₹35 each month, the fee decreases by ₹35 each month. Thus, the AP has first term ₹900 and common difference \(d=-35\). Therefore, \(a_{10}=900+(10-1)(-35)=900-315=₹585\). ₹550 would result from subtracting ₹35 ten times, but there are only 9 intervals from the first month to the tenth month. Exam tip: use \(a_n=a+(n-1)d\) for the nth term.