Video Transcript
If a card is drawn at random from a deck of cards that are numbered one to 30, what is the probability that it has a number that is not divisible by 10?
In this question, we are told that we have a deck of cards numbered one to 30 as shown. We are asked to find the probability that a randomly drawn card is not divisible by 10. We begin by recalling that any number that is divisible by 10 must be a multiple of 10, that is, 10, 20, 30, and so on. In this question, this corresponds to three of our cards. As three of the 30 cards are divisible by 10, 27 of them are not divisible by 10.
Writing this as a fraction, we have the probability that a randomly chosen card has a number that is not divisible by 10 is 27 over 30. This fraction can be simplified, as both the numerator and denominator are divisible by three. 27 divided by three is nine, and 30 divided by three is 10. So our fraction simplifies to nine over 10. We can therefore conclude that the probability in its simplest form is nine-tenths. We note that this could also be written as 0.9 or 90 percent.