Q. There were 20 students running in a race. How many different arrangements of first, second, and third place are possible?Answer:
Calculate Permutations Formula: To determine the number of different arrangements for the first three places, we need to calculate the number of permutations of 20 students taken 3 at a time. The formula for permutations is P(n,k)=(n−k)!n!, where n is the total number of items and k is the number of items to arrange.
Calculate Factorial of 20: First, we calculate the factorial of 20, which is 20!=20×19×18×…×1.
Calculate Factorial of 17: Next, we calculate the factorial of the difference between the total number of students and the number of places, which is (20−3)!=17!=17×16×15×…×1.
Use Permutation Formula: Now, we use the permutation formula P(20,3)=(20−3)!20!=17!20!.
Simplify Expression: We simplify the expression by canceling out the common factorial terms: P(20,3)=120×19×18=20×19×18.
Perform Multiplication: We perform the multiplication: 20×19×18=6840.
Final Result: Therefore, there are 6840 different arrangements of first, second, and third place possible among 20 students running in a race.