Question

Which term of the A.P. \(72,\,63,\,54,\,\ldots\) is zero?

• A. 8th
• B. 9th
• C. 10th
• D. 11th

Hint:

To find when an A.P. hits a target value \(T\), solve \(a+(n-1)d=T\).

Answer 1

The Correct Option is B

Step 1: Identify \(a,d\).
\(a=72,\ d=63-72=-9\).
Step 2: Set \(a_n=0\).
\(a_n=a+(n-1)d=72+(n-1)(-9)=0\).
Step 3: Solve.
\(72-9n+9=0 \Rightarrow 81-9n=0 \Rightarrow n=9\).