<p>Hi guys,</p>
<p>I need help with those 3 question they are from kaplan.</p>
<p>Pump 1 can drain a 400-gallon water in 1.2 hours. Pump 2 can drain the same tank in 1.8 hours. How many minutes longer than pump 1 would it take pump 2 to drain a 100-gallon tank?
1)0.15
2)1.2
3)6
4)9
5)18</p>
<p>Answer is D,but I don't understand why sometimes I have problems with these types of question thats why I need to understand its logic.</p>
<p>A typist typed the first n pages of a book, where n > 0, at average rate of 12 pages per hour and typed the remaining n pages at average of 20 pages per hour. What was the typist's average rate in pages per hour for entire book?
1)14
2)15
3)16
4)17
5)18</p>
<p>Answer is B,but I didn't understand the this question aswell.</p>
<p>Thanks in advance for your help.</p>
<p>A typist typed the first n pages of a book, where n > 0, at average rate of 12 pages per hour and typed the remaining n pages at average of 20 pages per hour. What was the typist’s average rate in pages per hour for entire book?</p>
<p>The book has 2n pages. It takes the typist n/12 hours to type the first n pages, and n/20 hours to type the remaining n pages. The average rate is therefore: number/time = 2n/(n/12 + n/20). Factor out the n’s. and simplify by multiplying numerator and denominator by 240, to get: 480/32 = 15.</p>
<p>Here’s a solution to the first question:</p>
<p>First let’s convert to minutes.</p>
<p>Pump 1 can drain a 400-gallon water in 1.2<em>60 = 72 minutes. Pump 2 can drain the same tank in 1.8</em>60 = 108 minutes. </p>
<p>Now divide these numbers by 4 to see the number of minutes for a 100-gallon tank.</p>
<p>Pump 1: 72/4=18
Pump 2: 108/4=27</p>
<p>Finally subtract: 27-18=9</p>
<p>A cheap way to solve the second problem is do 2xrate1xrate2/(rate1+rate2)</p>
<p>@DrSteve</p>
<p>But why divide by 4? I don’t get it?</p>
<p>Its divided by 4 bcuz it gives the rate of draining 400 gallons of water, but it only asks for the rate to drain 100 gallon</p>
<p>(400 gallons)/4 = 100 gallons.</p>
<p>ohhhhhhhh! Thanks :D</p>
<p>Isn’t anybody going to point out that the typist problem can be solved with Xiggi’s formula? It isn’t about driving, but you are still accomplishing the same task at two different rates, looking for the average rate. </p>
<p>So: 2 x 20 x 12 /(20 + 12) = 15</p>
<p>^ I did already haha</p>
<p>Thanks guys I understand both questions now.</p>