The standard deviation for the combined assignment is 5 minutes.
To combine the standard deviations, we use:

With our information, we have:
The top 4 firms have (23 +22 +18 +12)% = 75% of the market.
The 4-firm concentration ratio is 0.75 or 75%.
The banner would be 10feet 3inches
Answer:
A=115 B=65 C=115 D=65
Step-by-step explanation:
Hope it helps