Question

Which term of the AP:3,8,13,18,....is 78

Answer 1

Answer:

an = a+(n-1)d

78=3+(n-1)5

78-3=(n-1)5

75=(n-1)5

75/5=n-1

15+1= n

16=n

plz mark this answer best

78 will be 16th term

Answer 2

Answer:

16

Step-by-step explanation:

This is an AP. nth term of AP is given by a + ( n - 1 )d, where symbols have their usual meanings.

Here,  

a = first term = 3

d = comm. diff. = 8 - 3 = 5

Let the required number of terms be n.

⇒ 78 = 3 + ( n - 1 )5

⇒ 78 - 3 = ( n - 1 )5

⇒ 75 = ( n - 1 ) 5

⇒ 75/5 = 15 = n - 1

⇒ 15 + 1 = n

⇒  16 = n

Hence the required number of terms is 16

$\rule{110}2$