When Ms. Wade used the method described in parts 1 through 3, she picked 30 fish at first, marked them, and put them back in the bag. Ms. Wade thoroughly mixed the fish in the bag and randomly picked out 40 fish. Of these 40 fish, 5 were marked. The children in Ms. Wade's class had several different ideas for how to determine the total number of fish in the bag. For each of the following initial ideas, discuss the idea and describe how to use the idea to determine approximately how many fish are in the bag. Which ideas are related?
a. 40 40 40 40 40 40
↓ ↓ ↓ ↓ ↓ ↓
5 5 5 5 5 5

b. 40 -> 5
80 -> 10
120 -> 15
160 -> 20
200 -> 25
240 -> 30