CAT2 q22

[gmatwork]

On average, the bottle-nosed dolphin comes up for air once every two minutes; the beluga whale, a close relative, comes up for air on average once every five minutes. The number of times a bottle-nosed dolphin would come up for air in a 24 hour period is approximately what percent greater than the number of times a beluga whale would come up for air in that same period?



50%


100%


150%


200%


250%

OA:C

I could not understand this part of the MGMAT OE:-

"Since the both animals rate of coming up for air is an average, the relative number of times each comes up for air will be the same for any period of time. There is no reason to calculate the number of times either animal comes up over a 24 hour period."

Please explain how?

[tim]

i'm afraid i don't understand your question. the solution explains how, so can you be more specific about what you didn't understand in the solution?

[gmatwork]

"Since the both animals rate of coming up for air is an average, the relative number of times each comes up for air will be the same for any period of time. There is no reason to calculate the number of times either animal comes up over a 24 hour period."

Specifically, I don't understand why using average rate makes the relative number of times each animal comes up for air the same for any period of time. What is special about the average rate?

[jnelson0612]

"Since the both animals rate of coming up for air is an average, the relative number of times each comes up for air will be the same for any period of time. There is no reason to calculate the number of times either animal comes up over a 24 hour period."

Specifically, I don't understand why using average rate makes the relative number of times each animal comes up for air the same for any period of time. What is special about the average rate?

Yeah, I can see how this would be confusing. Think of it this way:
A dolphin comes up for air every two minutes
A whale comes up for air every five minutes

Thus, in ten minutes the dolphin will come up five times and the the whale will come up two times. This ten minute block will repeat itself over and over again in the 24 hours, with the proportions of the air breaks exactly the same throughout the 24 hours.

So here's our question: "The number of times a bottle-nosed dolphin would come up for air in a 24 hour period is approximately what percent greater than the number of times a beluga whale would come up for air in that same period?"

We can just substitute in "10 minutes" for "24 hours" and think the dolphin will come up 5 times and the whale 2 times. Thus the dolphin comes up 3 more times, and to calculate percent greater we put the difference over the SMALLER amount. Thus 3/2=150%. This is all the explanation was trying to say. I hope that this makes more sense now!

[gmatwork]

So if we can just do the calculation for "the least common multiple " amount of time ( in this case it will be blocks of ten minutes) ...should be fine?

[tim]

that's correct!