Do I add or divide or division or subtract?

Question

Assume there is national lottery and the winning ticket is worth $10 million. One winning ticket will be selected. If there are 125 million tickets sold, what is the chance that a buyer of one ticket will have the winning ticket?

Do I divided or do I division or add or subtraction?

Answer 1

chance of winning the top prize, given 125 million tickets sold is 1 divided by 125 million

= 1/125,000 = 8 x 10^-9 = 0.000000008 = 0.0000008% chance of winning

assuming no other winning smaller prizes, the expected value of purchasing 1 ticekt is 10/125 = 2/25 = 8 cents. If the ticket cost more than that, it's a losing bet, on average.

this all assumes 1 of the 125 tickets is the winning number, or that on average 1 of the 125 tickets will be a winning number