Consider the number of patients admitted in hospital A and hospital B to be 'x' and ‘x + 21'
Given that, the sum of recovery days for patients in hospitals A and B were 200 and 152, respectively.
The average recovery days for patients admitted in hospital A was 3 more than the average in-hospital B.
\(\frac{200}{x}=\frac{152}{x+21}+3\)
By solving the above equation we get x = 35.
Hence, the number of patients admitted to hospital A is 35.