The 9 stands for hundredths
Answer:
20%
Step-by-step explanation:
To find what percentage is $10 out of $50, we divide 10 by 50:

If we want to get the result in percentage form, we simply multiply it by 100%:

So a tip of $10 on a $50 bill is a tip of 20%.
f = (f1 f2) / (f1 + f2)
f(f1 + f2) = f1 f2
f f 1 + f f 2 = f1 f 2
f1 f2 - f f2 = f f1
f2 (f1 - f) = f f1
f2 = (f f1) / (f1 - f) <==== solution