9514 1404 393
Answer:
400%
Step-by-step explanation:
Suppose sales in 1954 were 500. Then 80% of that amount is 400. A drop of 400 puts sales in 1955 at 500 -400 = 100.
The increase back to 500 in 1956 is an increase of 400 from a base of 100. As a percentage increase, that is ...
400/100 × 100% = 400% . . . . increase from 1955 to 1956
