Question

Which term of the A.P. 3, 8, 13, 18, … is 78?

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Answer 1

Answer :

• 16th term is 78.

S O L U T I O N :

Given,

• A.P → 3, 8, 13, 18, … 78.

To Find,

• Which term of the A.P is 78.

Explanation,

Given,

• A.P → 3, 8, 13, 18, … 78.

Here,

• First term (a) = 3

• Common difference (d) = Second term - First term

→ d = t2 - t1

→ d = 8 - 3

→ d = 5

• Common difference (d) = 5

• a_n = 78

We know that,

nth term of an AP,

→ a_n = a + (n - 1)d

[ Put the values ]

→ 78 = 3 + (n - 1) × 5

→ 78 = 3 + 5n - 5

→ 78 = -2 + 5n

→ -5n = -78 - 2

→ -5n = -80

→ n = 16

Therefore,

The 16th term of this A.P. is 78.