Yes, definitely. If in some of solved problems in PM you will find that average beta is used but you can & should used weighted average beta. There is no reason your answer has to 'match' that of ICAI as long as you have done it the right way.
@ Mr. Sunil- Yes, PM has solved few sums by taking simple & weighted avg as well this was the reason for confusion.....anyways Thanks a ton sir for your valuable time giving.