Question

Which term of the Ap: 3,8,13,18.......is 78?​

Answer 1

Answer:

             $\bold{a_{16}=78}$

Step-by-step explanation:

$a_1=3,\ a_2=3+5=8,\ a_3=8+5=13,\ a_4=13+5=18\ \implies\ d=5\\\\a_n=a_1+(n-1)d\\\\a_n=3+(n-1)(5)\\\\a_n=3+5n-5\\\\a_n=5n-2\\\\ a_n=78\quad\implies\quad n=\,??\\\\78=5n-2\\\\78+2=5n\\\\5n=80\\\\n=16$