If zoey has a bag of marbles containing 18 red marbles, how many blue marbles should she add to the bag so that the probability of her drawing a blue marble from the bag is 1/4?

We would have to add enough blue marbles so that the red marbles are equal to 3/4 of the marbles in the bag. So we divide 18 by 3 which is 6. 6 is how many blue marbles we need to add to the bag. I hope this makes sense, let me know if you still need help!

Since it takes her 2 1/2 miles to get to the aquarium from her hotel, you need to subtract the various distances from  this value in order to find how long it took Clara to walk the rest of the way to the aquarium. 

2 1/2 - (1/4+1 3/4)= 2 1/2 - 2= 1/2

Clara must walk 1/2 a mile to get the rest of the way to the aquarium.