In a standard 52-card deck of playing cards, each card has one of four suits: spade, heart, club, or diamond. There are 13 cards of each suit. Alison thoroughly shuffles a standard deck, draws a card, then returns it to the deck, and shuffles again. She repeats this process until she has drawn seven cards. Find the probability that she draws at most two spade cards. Use a TI-83, TI-83 plus, or TI-84 calculator to find the probability.

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.