Combination & Probability (1)( Week 19 Practice) 1. There are 20 students. If every two students will talk on phone at least once during the summer vacation, at least how many calls will they make in total? 2. Using digits 1, 2, 3, and 4, how many different 3-digit numbers can you make if no digit can be used more than once within a number? 3. Using a die(a cube with number of 1 to 6), what is the probability of throwing a 2, 3 and 4 in the order? 4. A spinner shown in the diagram has 6 equal sections. The probability of the pointer falling into each section is the same (Assume the pointer will never fall on a line between two sections). What is the probability that the pointer falls on a number that is a multiple of 3?
5. Jennifer accidentally saved a valuable document into a computer with 50 folders. It is equally likely that the document is in any of these folders. If exactly 8 of these 50 folders are belonging to Jennifer, what is the probability that the document ended in one of her own folders? |