Michelle collects us, canadian and mexican stamps. in her collection 80% of the stamps are u. s. and mexican stamps. there are 3 times as many u. s. stamps as mexican stamps. what percent of michelle's collections is made up of u. s. stamps?

We know that 80% of the stamps are US and Mexican. 
The US stamps are 3 times the Mexican stamps. That means that of the 80%, Mexicans comprised of the 20% and US comprised of the 60% to satisfy the relationship of their ratios. 

Therefore, 60% of Michelle's collection is made up of US stamps.