Bunuel wrote:

The Fishery Diner at the start of business operations had lobsters and fish in a seafood tank in a ratio of 2 to 5. Over the first hour of operations no seafood was sold and lobsters were added to the tank. If after adding the two lobsters the ratio of lobsters to fish in the tank was 1 to 2, which of the following is the number of lobsters in the tank at the start of business operations?

A. 1

B. 2

C. 4

D. 8

E. 10

Instead of working with equations, we'll work with the answers.

This is an Alternative approach.

Let's start with the median - C.

If there were 4 lobsters at the start then there were 10 fish (as the ratio is 2:5).

Adding two lobsters changes this to 6:10 with is more than 1:2.

(C) is eliminated.

We have too few fish so we'll need to choose a larger number meaning that (B) and (A) are also eliminated.

(If you don't understand this it's OK - just try (B) and see for yourself)

Let's try (D): If there were 8 lobsters at the start then there were 20 fish.

Adding 2 lobsters gives a ratio of 10:20 = 1:2. Yes!

(D) is our answer.

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