Ted bought seven CDs. A week later half of all his CDs were destroyed in a fire. There are now only 20 CDs left. With how many did he start?

Answer: 33 CDs

Since half the CDs were destroyed, you need to find the total CDs Ted had before the fire.

20 CDs = 1/2 of what Ted had

20*2=40 CDs

Now, subtract 7 from the 40 CDs to find the amount he had in the beginning.

40-7=33

33CDs

20 is half. 40 he had after buying 7. 40-7 is 33.