Having in mind that what we need is to find people with less than 30 years old, no matter what gender. So we might proceed like this:
450 of them are female, and
1/2 of the females are less than 30 years old
Half of 450 is 225, that makes 225 participants younger than thirty years
On to the males... if 450 are females, then 300 are males (assuming you only have two genders of course ;) )
1/4 of the males are younger than thirty years and
A quarter of 300 is 75, that makes 75 more participants younger than thirty years.
And now what you need to do is to add them like this:
225 + 75 = 300 participants younger than thirty years...
The chance therefore of getting somebody younger than thirty is
300/750, or 2/5
or 40%
Hope this is good one to you
