In Rohan's birthday party, 90% of his friends came and 3 friends did not come. Find the total number of friends Rohan has.

Given: At Rohan's birthday party, 90% of his friends came and 3 friends did not come.

To find: We have to find the total number of friends Rohan has.

Solution: 

Let the total number of friends of Rohan = a

Given that 90% of his friends came so 10% of his friends didn't come.

10% of Rohan's friends = $a\ \times \ \frac{10}{100} \ =\ \frac{a}{10}$

It is also given that number of his friends did not come is three. So,

$\Longrightarrow \ \frac{a}{10} \ =\ 3$

$\Longrightarrow \ a\ =\ 30$

So Rohan has total 30 friends.