MATHS
posted by BRYAN .
Each Sunday the hymns to be sung are displayed on a hymnboard using numbered cards. The cards have the digits 0 to 9 on them. The hymn book has 750 hymns in it. Three different hymns are sung each service.
a) What is the smallest number of cards the church must have to be able to display any combination of 3 hymns?
b) If the number 6 can be used as an upsidedown 9, how many cards can be saved from your anwswers to (a)?

the first card: 17
the second card: 09
the third card: 09
I calculate so that is lets see, 28 cards?
YOu can save three two cards, the second set of 9's. 
Sorry, I'm still don't understand the suppose answer is a) 66 b) 4