In a bag, there are 10 yellow marbles and there are 9 red marbles. What is the probability of choosing an orange marble?

Question

In a bag, there are 10 yellow marbles and 9 red marbles. If the probability of choosing a yellow marble is 1/10, how many orange marbles are there in the bag?

 

Not sure how to figure this out. This question was on my Math Praxis. 

Answer 1

Alright, Taylor, remember that we always reduce probability to its lowest terms, so if there is a 3/6 chance, then we reduce it to a 1/2 chance, because 3/6 = 1/2.

 

If the probability is 1/10 of choosing a yellow marble and there are 10 yellow marbles, then we set 10/t = 1/10, with t being the total number of marbles in the bag, remembering that the probability is the 10 yellow marbles out of the total number of marbles.

 

If we cross multiply, we get t = 100, so the total number of marbles is 100.  If there are 10 yellow and 9 red, then there must be 81 orange marbles, because 10 + 9 + 81 = 100.

 

Hope this helps!