One half of your cds are scratched. one fifth will not play properly. you have 40 cds. how many will not work play properly

So the 1/2 of the CDs that are scratched and the 1/5 that will not play properly would be counted towards the "How many will not work play properly."

So, you just want to find 1/2 of the CD count, and 1/5 of the CD count, and add them together.

1/2 of the CD count:

Just multiply 1/2 by 40. 1/2 * 40 = 40/2 = 20

So 1/2 of the CD count = 20.

Then 1/5:

1/5 * 40

40/5

8

So 8 = 1/5 of 40.

Since the total would be those two added together, you would add 8 and 20 together.

8 + 20 = 28

960 ft would be the elevation change because you started at 100 feet below sea level. then you got to 220 ft above sea level. they said that you were 1/3 way up the mountain. so you add 100 with 220. that would equal 320. after that, you multiply 320 by 3 because you want to know how high it is from the bottom of the mountain to the top. so 320 times  3 equals 960. hope this : )