The correct answer is: C. $\frac{{{\text{Standard hours for actual production}}}}{{{\text{Actual hours worked}}}} \times 100$
The efficiency ratio is a measure of how efficiently a company uses its resources. It is calculated by dividing the standard hours for actual production by the actual hours worked. A higher efficiency ratio indicates that the company is using its resources more efficiently.
Option A is the number of actual working days in a period divided by the number of working days in the budget period. This is not a measure of efficiency, as it does not take into account the number of hours worked.
Option B is the actual hours worked divided by the budgeted hours. This is a measure of efficiency, but it does not take into account the standard hours for actual production.
Option C is the standard hours for actual production divided by the actual hours worked. This is the correct measure of efficiency, as it takes into account both the actual hours worked and the standard hours for actual production.
The efficiency ratio can be used to compare the efficiency of different companies or to track the efficiency of a company over time. It can also be used to identify areas where a company can improve its efficiency.