Word problem help.

Question

A group of students are working on a project. They complete 30% of the project in 12 hours. If they continue to work at the same speed, how many howrs will it take the group to finish the project.

Answer 1

30%/12=100%/x where x=# of hours to finish the project

0.3/12=1/x

3/120=1/x

cross multiply

1(120)=3(x)

120=3x

x=120/3

x=40 hours to finish the project

another way to look at the problem...

30% finished in 12 hours

10% is 1/3 of 30%, so 10% is finished in (1/3)(12)=4 hours

100% is equal to 10*10%

so we need 10*4 hours=40 hours again