Hello dear, 

In order to take admission in IIM, you have to clear: 

1) common admission test( cat) 

2) after clearing cat, you have to give written ability test ( wat) and personal interview(pi). 

The student must have a bachelor's degree with a minimum of 50% for general category. So you can take either commerce with maths or science because that will help you very much in future. 

For more information, visit: 

https://bschool.careers360.com/articles/iim-admission-criteria-2018-20?amp

All the best!