# Find how ma

The two-digit numbers that are divisible by 7 are 14, 21,….. ,98

Here, First term = a = 14

Common difference d = 21 – 14 = 7,

Last term = an = 98

Since, nth term is given by:

an = a + (n - 1) d

98 = 14 + (n – 1)7

98 = 14 + 7n – 7

98 = 7 + 7n

91 = 7n

n = 13

There are 13 two-digit numbers divisible by 7.

OR

We know sum of n terms of an AP is:

Sn = n2

For n = 1,

S1 = 12

= 1

For n = 2,

S2 = 22

= 4

For n = 3,

S3 = 32

= 9 Now S1 = a1

a1 = 1

S2 – S1 = a2

4 – 1 = a2

3 = a2

Now, d = a2 – a1
= 3 -1

= 2

We know, an = a + (n – 1)d

For n = 10,

a10 = 1 + (10– 1)2

= 1 + 9(2)

= 1 + 18

= 19

So, 10th term of the AP is 19.

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