Tiffany collects perfume bottles. She has 99 bottles in her collection. Two thirds of her perfume bottles are made of crystal. How many of the perfume bottles in Tiffany's collection are made of crystal?

To find the number of perfume bottles that are made of crystal, multiply 99 by 2/3.

An easy way to do this in your head is to divide 99 by 3, and then multiply it by 2.

99/3=33

33*2=66

66 bottles in Tiffany's collection are made of crystal.