以下是一到关于折旧的一道很简单的题，请大家帮忙看一下：

Santa runs a large toy shopm In the year ended 31 August 2005. SHe bought the following fixed assets:

A new cash register for $5,000. this was purchased on 1 December 2004, and was to be depreciated at 10% straight line

A new delivery van, purchased on 31 March 2005, at a cost of $22,000. the van is to be depreciated at 15% reducing balance.

Santa charges depreciation on a monthly basis

What is depreciation charge for the year ended 31 August 2005?

讲义上的答案如下：

Cash register   10%*5,000*9/12=375

Delivery van     15%*22,000*5/12=1,375

我的疑问是： Delivery van depreciation is charged by reducing banlance method as mentioned, why does it use the straight line method to calculte?