Question

There are 30 numbers greater than 20 and less than 51 out of which numbers are multiple of 9, And numbers have 7 as one of their factor.

Answer 1

First let us see multiples of $9$ between $20$ and $51$
$9\times 2=18$
$9\times 3=27$
$9\times 4=36$
$9\times 5=45$
$9\times 6=54$
Their are $3$ multiples of $9$ between $20$ and $51$.i.e $27,36,45$.

Now, the numbers having $7$ as one of their factor will be multiples of $7$.
So, finding out the multiples of $7$ between $20$ and $51$ we get,
$7\times 3=21$
$7\times 4=28$
$7\times 5=35$
$7\times 6=42$
$7\times 7=49$
Their are $5$ numbers between $20$ and $51$ which are multiple of $7$ or they have $7$ as their factor.