what is the formula used when we want to know the interest when fixed amount is withdrawn 'half yearly'???

Hey Diksha, the solution to your this query is already covered in the Study Material provided to you on our site. To view, follow the link given below. 
https://www.meritnation.com/cbse/class12-commerce/studymaterial/accountancy/partnership-accounts/accounting-for-partnership--basic-concepts/435_2429_7810#slide5_interest-on-partners-drawings