Step-by-step explanation: She gave her sister one fifth of the collection; one fifth written as a percent is 20% (I did one and divided it by five). To turn 20% to a decimal I didved by 100 to get 0.20. I multiplied 200 and 0.20 and got 40. 40 is the amount of shells given to her sister, so you would subtract 40 from 200 to find how many shells were left. 200-40=160.
