25% of what number is 9​

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?

Arestaurant gives out a scratch-off card to every customer. the probability that a customer will win a prize from a scratch-off card is 25%. design and conduct a simulation using random numbers to find the experimental probability that a customer will need more than 3 cards in order to win a prize. justify the model for your simulation, and conduct at least 10 trials.

Simplify. (-2)^-3 a. -8 b. -1/8 c. 1/8 d. 8