Class 10

Math

All topics

Sequences and Series

How many two–digit numbers are divisible by 3?

let them be $a_{1},a_{2},a_{3}……$and so on

$a_{2}−a_{1}=15−12=3$

$a_{3}−a_{2}=18−15=3$

so,

and we also know last term of series $=99$

now,$a_{n}=a+(n−1)d$

$99=12+(n−1)3$

$87=(n−1)3$

$n=30$

$99$is the 30th term

$∴$ total terms are 30

answer