how do you do this kind of question

Test Preparation SAT Preparation
1

<li>If Sam can do a job in 4 days that Lisa can do in 6 days and Tom can do in 2 days, how long would the job take if Sam, Lisa, and Tom worked together to complete it?</li>
</ol>

<p>A. 0.8 days
B. 1.09 days
C. 1.23 days
D. 1.65 days
E. 1.97 days</p>

<p>thanks.</p>

2

<p>rate times time equals work. rt=w and r=w/t</p>

<p>sam’s rate = 1 job/4 days = 1/4
lisa’s rate = 1 job/6 days = 1/6
tom’s rate = 1 job/2 days = 1/2</p>

<p>(1/4 + 1/6 + 1/2)t = 1
11/12t = 1
t = 12/11 = 1.09 = B</p>

3

<p>Just to explain what Noitaraperp did:</p>

<p>Sam does 1/4 of a job per day
Lisa does 1/6 of a job per day
Tom does 1/2 of a job per day</p>

<p>In total they do 11/12 of a job per day</p>

<p>This means that in 12 days they could do 11 jobs</p>

<p>So to found days per job (days/job)</p>

<p>Divide 12/11 = 1.09 days to do one job</p>