Question

Find the number of all 2 digit numbers divisible by 3 and 5

Answer 1

30 60 90 15 45 75 .........

Answer 2

$two \: digit \: no \: divisible \: by \: 3 \: and \: 5\: are \: \: \\ 15.30.45.60.......................90 \\ a = 15 \\ d = 15 \\ an = 90 \\ 90 = 15 + (n - 1)15 \\ 90 =15n \\ n = 6 \\ s6 = \frac{6}{2} (2 \times 15 + (6 - 1)15) \\ = 3(30 + 5 \times 15) \\ = 3(30 + 75) \\ = 3 \times 105 \\ = 315$