Racehorse TALK

My daughter is in grade 8 and is doing some probability in maths.

She asked for some help with an assignment that included some questions about a raffle.

The raffle has 36 tickets that cost 80 cents each. The person running the raffle wants to make a profit of $22.

They had to first workout what the total revenue from the raffle was ie $28.80

Then what the prize needed to be for the promoter to make their profit ie $6.80

They then had to do up a table showing the probability of winning if buying 1 to 10 tickets, the cost of the tickets  and the profit you would make if you bought those tickets and won, ie

1 ticket - cost 80c - 1/36 chance of winning - profit $$6.00
2 tickets - $1.60 - 1/18 - $5.20
3 tickets - $2.40 - 1/12 - $4.40
4 tickets - $3.20 - 1/9 - $3.60
5 tickets - $4.00 - 5/36 - $2.80
6 ticket - $4.80 - 1/6 - $2.00
7 tickets - $5.60 - 7/36 - $1.20
8 tickets - $6.40 - 2/9 - $0.40
9 tickets - $7.20 - 1/4 - loss 0.40c
10 tickets - $8.00 - 5/18 - loss $1.20

So far so good.

The next question was, how many tickets should you buy and why?

My daughter told me she didn't need help with this bit because they had discussed it in class.

Good I said, can you tell me why the amswer is zero?.

What? She gives me a funny look and tells me the answers not zero it's 6.

What!!!!!!!!!!!!!

How can it possibly be 6 I ask.

The teacher said that you shouldn't buy 9 or 10 because you still lose if your ticket comes out, and 1 or 2 doesn't give you enough chance of winning. 6 is right because it gives you a good chance of winning a good amount.


A brief summary of my response is it included some not very complimentary comments about the education system, a discussion of negative expectation and rational behaviour and me fronting the teacher on Monday morning for an explanation.

My daughter is of course horrified at the thought of me contacting her teacher. I've met the teacher at parent-teacher interview night and he seems a nice enough fellow, my daughter really likes him and we actually give him credit for her getting her first ever A in maths. My partner says I should let it go, it's not that important and it's not worth causing my daughter grief or embarrassment at school. I'm still dumbfounded and a bit outraged.

So, what do you reckon? Do I make a case of it or not?