The answer would be 18/20 or simplified, 9/10. You do that by finding the product of the 2 numbers. In this case it would be 4 times 5 which is 20. The denominators has to be the same, so 2/5 times 4 is 8/20. 2/4 times 5 equals 10/20. Now 8/20 plus 10/20 equals 18/20, or 9/10. There's your answer.