alleryStart learning →Which term of the AP $3,\ 8,\ 13,\ 18,\ \ldots$ is equal to $78$?
A16th
B14th
C15th
D18th
Answer & Solution
Correct answer: A. 16th
1. a = 3, d = 5. Set $a_n = 78$: $3 + (n-1)5 = 78$.
2. $(n-1)5 = 75 \Rightarrow n-1 = 15 \Rightarrow n = 16$.
3. So the **16th term** is 78.
_Source: Karnataka SSLC (KSEEB) Class 10 Mathematics, Ch1 'Arithmetic Progressions' (nth term)_
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