## Whale & dolphin probability (percentage)

 Difficulty: Rating: GCSE Marks:

GCSE Text:
Stefan chooses to go on a whale and dolphin watching boat trip in Spain.  The trip is advertised as having a probability of seeing dolphins as 50%.  Whether or not guests see whales, the probability of seeing whales is advertised as 90%.

a) Draw a probability tree diagram to represent this information

b) What is the probability of Stefan seeing both whales and dolphins on his trip?

c) What is the probability of Stefan seeing at least whales or dolphins on his trip?

Suggestions:
Both Foundation & Higher GCSE papers now have probability questions, so students needs to be able to understand simple probability and ideally be able to complete and interpret a probability tree diagram. This is one of two videos, the other having a similar problem but with probabilities expressed as fractions. This works well as a consolidation task in class. Works well as a springboard for reminding of the different processes as you work left to right across the tree diagram.  Worth waiting until the ‘We Need Maths’ logo on this video – almost every students asks ‘did you see whales or dolphins’?

Extension Ideas:
Teachers could extend the learning by considering:

• The boat company offers a ‘free trip’ to guests who see neither whales or dolphins on their trip.  If the company runs 5 trips per day for 300 days of the year. On how many trips per year are people likely to see no whales and no dolphins?