If mass of the planet is 10% less than that of the earth and radius of the planet is 20%
greater than that of the earth then the weight
of 40kg person on that planet is

25kg

Explanation:

The formula for acceleration due to gravity is:

Here, G represents a constant and M represents the mass of the object. We don't need to know the actual values to solve this, then: We can just multiply by the amount they are multiplied relative to earth.

Multiplying this by the weight of the person on Earth of 40kg, you get 0.625*40=25kg.

Hope this helps!