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how is this a % change question?

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how is this a % change question?

by abcdefg » Fri Jul 10, 2009 7:59 am
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%

[spoiler] The OA is C 150%. basically 5-2/2. My question is, how is this a percent change question? Doesn't "What % greater" mean 5/2"? [/spoiler]. Thanks.
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by truplayer256 » Fri Jul 10, 2009 8:05 am
The total number of minutes in 24 hours = 24 * 60= 1440 minutes

The number of times the bottle nosed dolphin comes up for air= 1440/2=720 times

The total number of times the beluga whale comes up for air= 1440/5=288 times.

288*x/100=720

x=250%= PERCENT INCREASE= 250%-100%=150%<--- You always have to subtract 100% from this to find the amount of percent increase%. Remember that 100% is the original number that you had before.

Another way to find percent increase:

(Higher number- lower number)/ lower number=([720-288]/288)*100= 150% increase.
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by jjk » Fri Jul 10, 2009 10:52 am
You can easily solve this by setting the time frames equal to each other at 5 minutes.

If the dolphin comes up for air every 2 minutes, it will come up for air 2.5 times every 5 minutes.

1/2 = 2.5/5

We already know that the beluga comes up for air every 5 minutes.

1/5

With the time frames equal, we can easily solve for the percent difference.

(2.5 - 1)/1 = 1.5 = 150%

OA is C
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by jjk » Fri Jul 10, 2009 10:53 am
So the key take-away here is to not use extra calculations and bigger, unwieldy numbers if you don't have to.
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by ghacker » Sat Jul 11, 2009 9:48 am
This is a proportionality issue , Think as if you are doing some rate problem

Answer is 150% 0r 3/2

Or LCM (2,5) =10 so very 10 min they surface together , but in 10 min one has come up 5 times and the other only two

Hence ans = (5-2)/2 % =3/2% =150 %
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by abcdefg » Sat Jul 11, 2009 11:03 am
Hi everyone, thanks for putting out the solution. I knew how to answer the question but I wasn't sure what they were asking. The question asked,

"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?"

I thought what % greater is just asking for (5/2) rather than (5-2)/2.
For example when someone says 9 is what % greater than 3, isnt the answer (9/3) = 300% rather than (9-3)/3 = 200%?
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by abcdefg » Tue Jul 14, 2009 11:58 am
can someone help me clarify this question please? The practice questions seem to be mixing them 2 up: the difference between percent increase and percentage point increase.

A) 3% - 2% = 1%.
B) 3% is 100% greater than 2%.

I just don't know when to do A vs B.
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by GID09 » Tue Jul 14, 2009 1:42 pm
Hi abcdefg, You could look for the words such as "% greater than or % increase" to decide if you need to use % change i.e 5-2/2 = 150% .If the question X is what % of Y, then use the fraction i.e 5/2 = 2.5. So dolphin and blue whale comes out to the surface in the ratio 5:2 and dolphin comes 5-2/2 = 150% MORE/GREATER THAN blue whale for a given time period.

Hope this helps!
GID09
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