If a microwave oven produces electromagnetic waves with a frequency of 2.70 ghz, what is their wavelength?

Ok this one is pretty straight forward :) This is what we know:

1. 2.7GHz is how many vibrations in 1 second. (2.7 x10^9 Hz)
2. Light always has a constant speed 2.9 x10^8 meters per second.

Therefore to find out the length of one of those vibrations you just divide        2.9 x10^8 by 2.7 x10^9
which looks like this in your calculator:
290000000 / 2700000000
= 0.107m
= 10cm

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.

The answer is  a.first and third quarters