How do I calculate this percentage?

I am trying to calculate what the percentage would be in this scenario. I am borrowing 50k from an investor. and returning 70k back in 23.3 months. Basically a 20k profit in a little under 2 years. What percentage has the investor earned on his original 50k investment? And how do I arrive at the right percentage?How do I calculate this percentage?
70/50 --%26gt; 1.4 - 1 (what you borrowed) = .4 ---%26gt; 40% (interest)How do I calculate this percentage?
He originally gave you 50,000 and he will receive 70,000 back. So we need to find out what percent of 50,000 is 70,000. Lets say the percent is X.



50,000 * X = 70,000

X = 70,000 / 50,000

X = 1.4



Now lets just convert that to percentage and we get 140%, so he will get 40% more of his money back after the 23.3 months.How do I calculate this percentage?
Use the following formula in Excel:

=RATE(23.3/12,0,50000,-70000)



Answer: APR = 18.9%