The marks of 40 students in a test are shown in the table…

Step 1. The class marks. For $41$ to $50$ the class mark is $\dfrac{41 + 50}{2} = 45.5$. The class marks are $35.5, 45.5, 55.5, 65.5, 75.5$ and $85.5$.

Step 2. The products. $fx$ is $106.5, 273, 666, 655, 453$ and $256.5$. Their sum is $\sum fx = 2410$.

Step 3. The mean. $\bar{x} = \dfrac{2410}{40} = 60.25$ marks.