For this case, the first thing we must do is define variables. x: amount of time Miguel uses to complete the task. y: amount of time Maria uses to complete the task. We write the system of equations: x + y = 60 y = (1/2) x Solving the system we have: x = 40 minutes y = 20 minutes Answer: it take her to wash them by herself about: y = 20 minutes
Because there are 26 Letters, there are 25 possibilities for the first letter, and 10 choices for the numbers, so: 25*26*26*10*10*10 Multiply: 650*26*1000 16900*1000 There are 16,900,000 possibilities