Answer:
10 lbs
Step-by-step explanation:
Amount of coffee of 20$/lb = x lb
Its cost =20*x $
Cost of other coffee =80*50=4000 $
Total amount of coffee = (x+50) lb
The final mixture costs =70$/lb
Total cost of the mixture =(x+50)*70
So,
We have the equation
(x+50)*70=20*x +4000
50*x = 500
x=10
So, amount of 20$/lb coffee = 10 lb