Posted by Tao on .
Half the pupils in Mrs. Cross's class are boys. Half the boys have blue eyes. Half the blue-eyed boys have blond hair. There are three boys with blue eyes and blond hair in Mrs.Crooss's class. How many pupils are there total in that class.
"There are three boys with blue eyes and blond hair in Mrs.Cross's class."
Start with 3.
"Half the blue-eyed boys have blond hair."
So the above number of 3 only represents half of the blue-eyed boys.
So, there are 2*3 blue-eyed boys total, which is 6.
"Half the boys have blue eyes."
Now we can determine that there are 6*2 boys total.
Try to determine how many pupils are in the class.