F5 Dec 2012 exam question 2

I am puzzled with the answer published:

For question 2

(1) Regarding the planning and operational variance, i was taught using formula:

For instance, labor rate planning variance = (Standard rate – Revised standard rate) x Revised standard hour on actual output
However, according to the answer, (Revised rate – std rate) x actual hours paid is used.
Which formula is correct?

(2) When we say a process is 20% slower, do we mean it is only operates at 80% efficiency?
If operates in 100% efficiency we need to take 0.5 hours to complete, in 80% efficiency we will need to take 0.5 x 100/80 = 0.625 hours to complete.

So when a process is 20% slower, time taken should have increased 25%.

Using 0.5 x 1.20 = 0.6 hours does not make sense to me. Can anyone please enlighten me with this?