Entrance exam

Dean finishes his exam strongly. Can you work out how many questions are on the paper if he gets an average of 80%?
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem



In a university admissions test, Dean gets exactly 10 of the first 15 questions correct.

He then answers all the remaining questions correctly.

Dean finds out he has answered 80% of all the questions correctly.

How many questions are there on the test?

This problem is taken from the UKMT Mathematical Challenges.