Depreciation

Good day

Question 8.5 in the BPP revision kit 2020 – 2021

My question is:
Am I to assume that buildings use an estimated useful life of 50 years when first purchased if not given the useful life info or a way to calculate the original useful life info?

I got the question correct but I know the method I used would not work if I don’t have options to choose from. I know it is not what you taught us in your lectures.

I could not determine the original useful life used on the building to calculate the carrying amount for me to calculate the amount for the revaluation surplus so this is how I went about the question.

I calculated the depreciation charge for the year:
1mil divided by 40 years (revalued amount divided by remaining useful life) = $25,000

That left 2 options, A or B
For the revaluation surplus, I know it could not be A because the surplus is calculated, Revalued amount less the carrying amount at date of revaluation hence I chose B.

The answer in the book indicate the building was already depreciated for 10 years, this assumes that the original estimated useful life was 50 years. I just want to confirm if this is expected. I want to be able to get my answer correct when I don’t have options to choose from.

Sir, thank you in advance for your time and patience.