Question ''Rupab co'' and capital allowances

Hello mr admin!!!
I have some concerns regarding the question Rupab Co.
Here is a the paragraph that i am intrested in:
”Rupab Co pays taxation one year in arrears at an annual rate of 25%.Capital allowances on machinery are on a straight-line basis over the life of the asset.”
Earlier the question says that the project costs 2,5 milion and there is no scrap value at the end of the project that lasts 5 years.
To my understanding 25% depreciation on a straight-line basis implies 4 years not 5 years and the answer in the question states 5 years . 2,500,000 divided by 5 (the number of years) 500,000 and than the tax allowance 25% which gives us 125,000 over (again) 5 years.
I just don’t understand the logic behind it .
Can you please explain it to me.
Many thanks