if Sarah work for 4 hours alone. Rebecca and Isaac work for 3 hours. Sarah and Isaac work for 2 hours. how long will Rebecca work for.

Question

if Sarah work for 4 hours alone. Rebecca and Isaac work for 3 hours. Sarah and Isaac work for 2 hours. how long will Rebecca work for.

Answer 1

Here is a nice way to organize the information in a math problem like this, so you can solve more complicated versions of these problems later.  

 

Make a table

 

Name         |     Hours Worked

_________________________

Sarah         |      4    0    2

-----------------------------------

Rebecca      |      0    3    0

-----------------------------------

Isaac          |      0    3    2

 

 

Note how the table has 3 numbers for each person....each column under hours worked is for a sentence of the problem...The first sentence says Sarah works ALONE for 4 hours, meaning Rebecca and Isaac work 0 hours.  You can see how the second and third columns represent Rebecca and Isaac working 3hrs together and Sarah/Isaac 2hrs together.  

 

To find the # of hours worked by a person, add or sum, across the row that represents the person whose name is at the front of the row. For Rebecca this is 3, for Isaac it is 3+2=5 and for Sarah it is 4+2=6.

 

Another good use for a table like this is that we can figure out how much total work is accomplished by each "sentence" in the problem.  Assuming the sentences are chronological (in times sequence), we can see that 4 hours of work is done first by Sarah alone...then next 6 hours of work is done by a team of Rebecca/Isaac, and lastly 4 hours of work is done by the pair of Sarah/Isaac.  These numbers are the sums of the columns.

 

Using a table like this can often help solve a problem, and once you are practiced with these scenarios, you can develop your own notation for tracking the information as you read it in a paragraph.

 

Hope this helps...