Answer:
74.29%
Step-by-step explanation:
A student passed 60%, or a proportion of 0.60 of the 20 quizzes he's written so far. This means he has passed [tex]0.60*20=12[/tex] quizzes so far.
Now he has written 50 quizzes and passed 80% of them, or [tex]50*.8=40[/tex] quizzes.
To find the success rate, take the number of quizzes passed and divide by total number of quizzes.
[tex]\frac{Passed}{Total}[/tex]=[tex]\frac{12+40}{20+50}[/tex]=[tex]\frac{52}{70}[/tex]=.7429
To get a percentage, multiply this proportion by 100 to get 74.29%