Teacher looks at 4 tests in 35 minutes, how much time does it take him to look at 45 tests?

Question

Teacher looks at 4 tests in 35 minutes, how much time does it take him to look at 45 tests?

 

I think it goes something like this:

 

35min....4 tests

X min....35 tests 

 

but I'm not sure how this process is called.

Thanks so much.

Answer 1

set up a proportion

4/35=45/x

cross multiply

4x=35*45

4x=1575

x=1575/4

x=393.75 minutes

or,...

35/4=8.75 minutes per test

8.75*45=393.75 minutes