Hi Varun

The way the roles system works is tricky and discussed here - it involves weighting calculations for the context level - the lower the context the more weight and multiplying this to the sum of the permissions (inherit = 0, allow = 1, prevent = -1, prohibit = -1000) together 

To change the values you can

1) remove the user from learner role in the course, or
2) add overrides for limited learner role in the activity, or
3) assign them a learner's role in the activities

To make the appropriate role win you need to compare the calculations.

regards