A chef had 500 eggs. 10% of them were rotten. He used 3/5 of the
remaining eggs to bake cakes. How many eggs did the chef have left?
number not rotten = .9 * 500 = 450
number used = (3/5) * 450 = 270
number left over = 450-270 = 180
or, in one step:
number left over = .9 * 500 * 2/5 = 180