algebra
posted by Sean .
This is a project called guess your card. there are 3 people playing and you. We are drawing only numbers from 1 to 9. Each person draws 3 cards and puts them on their foreheads facing out. 1 has a 1,3,7 next person has 3,4,7 and 3rd person has 4,6,8. What cards do I have. What formula can I use to calculate this?

How many total cards are there? Since you talk about a 1 rather than an ace, I assume it is not a regular playing deck. If there are only 18, you can eliminate 3, 4 and 7. Since they don't have a 2, 5 or 9, that would be my best guess.
I don't know the formula/equation.