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

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

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Solution

3, 8, 13, 18, …

For this A.P.,

a = 3

d = a2 − a1 = 8 − 3 = 5

Let nth term of this A.P. be 78.

an = a + (n − 1) d

78 = 3 + (n − 1) 5

75 = (n − 1) 5

(n − 1) = 15

n = 16

Hence, 16th term of this A.P. is 78.

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APPEARS IN

NCERT Class 10 Maths
Chapter 5 Arithmetic Progressions
Exercise 5.2 | Q 4 | Page 106
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