Question

which term of the AP 3,8,13,18,.... is 78???​

Answer 1

$\boxed{ \underline{ \underline{❥\footnotesize \tt \blue{ \: Given:- }}}}$

$\: \: \: \: \: \: \: \: \: \: \: \: \:$

$\footnotesize \tt{a = 3}$

$\footnotesize \tt{d = 5}$

$\footnotesize \tt{an = 78}$

$\: \: \: \: \: \: \: \: \: \: \: \: \:$

$\boxed{ \underline{ \underline{❥\footnotesize \tt \blue{ \: Find:- }}}}$

$\footnotesize \tt{n = ?}$

$\: \: \: \: \: \: \: \: \: \: \: \: \:$

$\boxed{ \underline{ \underline{❥\footnotesize \tt \blue{ \: Solution:- }}}}$

$\: \: \: \: \: \: \: \: \: \: \: \: \:$

$\footnotesize \tt{an = a + (n - 1)d}$

$\footnotesize \tt{78 = 3 + (n - 1)5}$

$\footnotesize \tt{78 - 3 = (n - 1)5}$

$\footnotesize \tt{75 = (n - 1)5}$

$\tt{ \frac{75}{5} = \: } \footnotesize \tt{ (n - 1)}$

$\tt{ \cancel\frac{75}{5} = \: } \footnotesize \tt{ (n - 1)}$

$\footnotesize \tt{15 = (n - 1)}$

$\footnotesize \tt{15 + 1 = n }$

$\boxed{ \underline{ \underline{\footnotesize \tt{❥ \: 16 = n }}}}$

Answer 2

Answer:

an=a+(n−1)d

\footnotesize \tt{78 = 3 + (n - 1)5}78=3+(n−1)5

\footnotesize \tt{78 - 3 = (n - 1)5}78−3=(n−1)5

\footnotesize \tt{75 = (n - 1)5}75=(n−1)5

\tt{ \frac{75}{5} = \: } \footnotesize \tt{ (n - 1)}

5

75

=(n−1)

\tt{ \cancel\frac{75}{5} = \: } \footnotesize \tt{ (n - 1)}

5

75

=(n−1)

\footnotesize \tt{15 = (n - 1)}15=(n−1)

\footnotesize \tt{15 + 1 = n }15+1=n

\boxed{ \underline{ \underline{\footnotesize \tt{❥ \: 16 = n }}}}

❥16=n