measurement
posted by marko on .
a floor plan has a scale of 2cm : 3m
what is the actual length of a room measuring 30 cm on the floor plan?
I got to 20 is that correct?

Nope.
How have you been taught to solve this kind of problem?
I can show you two different ways. 
i cant figure how to do this can you explain

is it 90
i got
2cm/ 3m = 30 cm/n
= 2n = 3 (30)
= n = 90 
One way to do this is to set up a proportion or ration.
2 cm is to 3 m as 30 cm is to ? m
2/3 = 30/x
Cross multiply and solve for x.
2x = 90
Divide both sides by 2.
x = 45 m