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4MA1/1F Nov 2021, Question 15: Basic Probability

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1F (Foundation) · Calculator · 4 marks

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The question, in short

A tank holds 54 fish, white and red. A random fish has white probability 4/9. Find the original white count, then after adding white fish the probability becomes 1/2; find how many were added.

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Part (a) · 2 marks

Using 54 fish and white probability 4/9, work out how many white fish were originally in the tank.

  1. 1White fish = 4/9 of 54
  2. 254 ÷ 9 = 6, then 6 × 4 = 24

Answer24

Part (b) · 2 marks

After returning the fish and adding some white fish, the white probability is 1/2. Work out how many white fish were added.

  1. 1Red fish = 54 − 24 = 30, and no red fish are added.
  2. 2A probability of 1/2 means white = red, so there are now 30 white fish.
  3. 3White fish added = 30 − 24 = 6

Answer6

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