Learning Curve Question – Please help!

Hi All,

I was wondering if someone could help me with a question I am very stuck on please. I seem to be okay with most learning curve questions but this one has completely thrown me, please see below.

Batch Number: Time Taken:

1 100 minutes
2 70 minutes
3 59 minutes
4 55 minutes

What was the rate of learning closest to? (1.d.p)

The answer is 84.3% but I can’t get my head round the reasoning for this when I look at the answer. One method seems to be to take the average of the two learning rates of batch number 2 and 4.

Any help would be much appreciated!!

Thanks.