Dear Student
If per annum is not added with the percentage of depreciation, then no. of months have to be ignored and depreciation for the whole year is to be calculated. Say. If Depreciation is 10% for the year ending 31st March 2019 and machinery costing Rs 1,00,000 was purchased on 1st January 2019, then depreciation will be 10%*1,00,000= Rs 10000
Regards