Question
Which term of the AP: $3, 8, 13, 18, ………..,$ is $78$
✓
Answer
The given AP is $3, 8, 13, 18, .....$
Here $a = 3$
$d = 8 - 3 = 5$
Let the nth term of the AP be 78.
then, $a_n = a + (n - 1) d$
$ \Rightarrow 78 = 3 + (n - 1) (5)$
$ \Rightarrow 5(n - 1) = 78 - 3$
$ \Rightarrow 5(n - 1) = 75$
$ \Rightarrow n - 1 = \frac{{75}}{5}$
$ \Rightarrow n - 1 = 15$
$ \Rightarrow n = 15 + 1$
$ \Rightarrow n = 16$
Here $a = 3$
$d = 8 - 3 = 5$
Let the nth term of the AP be 78.
then, $a_n = a + (n - 1) d$
$ \Rightarrow 78 = 3 + (n - 1) (5)$
$ \Rightarrow 5(n - 1) = 78 - 3$
$ \Rightarrow 5(n - 1) = 75$
$ \Rightarrow n - 1 = \frac{{75}}{5}$
$ \Rightarrow n - 1 = 15$
$ \Rightarrow n = 15 + 1$
$ \Rightarrow n = 16$
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