If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55, 60, then the average marks of all the students is:

The total marks scored across all three batches can be calculated using the weighted average formula:
$$\text{Total Marks}=(55\times 50)+(60\times 55)+(45\times 60)$$

$$55\times 50=2750$$

$$60\times 55=3300$$

$$45\times 60=2700$$

$$\text{Total Marks}=2750+3300+2700=8750$$

Total number of students across all batches:

$$\text{Total Students}=55+60+45=160$$

Therefore, the combined average marks are:

$$\text{Average}=\frac{8750}{160}=\frac{875}{16}\approx 54.6875$$