Thread: a couple easy questions - factoring and word problem

1. Factor: 7x^2+26xy-8y^2

The answer is (7x-2y)(x+4y) but I can't figure out how!

2. Bernard and Carolyn are refinishing a table. Working alone, Bernard can do the job in 7 hours. If the two work together, the job take 3 hours. How long will it take Carolyn to refinish the table if she works alone?

So far, I have (1/7)(3) + (1/x)(3) = 1

There are several ways to approach problem number 2. This is my approach

Benard takes 7 hours to finish a table
Benard takes 21 hours to finish 3 table

Benard and carolyn takes 3 hours to finish a table
Benard and carolyn takes 21 hours to finish 7 tables

Since Benard takes 21 hours to finish 3 table
and Benard and carolyn takes 21 hours to finish 7 tables
Therefore Carolyn 21 hrs takes to finish 4 table
carolyn takes 21 / 4 = 5.25 hrs to finish 1 table