Here is the math question.
A 100m cliff erodes by 2/7 of its height each year.
(a) What will the height of the cliff be after 10 years?
This is how I worked out the question.
3.46m to 2d.p.
However my teacher said that it is wrong (to the whole class and also insulted me a bit >_>) and that I didn't follow this formula.
Tn = ar^(n-1)
And that I should have done
Which is instead
4.84m to 2d.p.
This doesn't make sense because if you used the formula and the question was
What will the height of the cliff be after 1 year?
100(5/7)^(1-1) =100(5/7)^0 =100
That doesn't make sense at all!
Am I right or is the teacher right?
ADDITIONALLY my teacher said his answer is an interpretation of the question. Is his answer a valid interpretation of this question? Or is it just incorrect mathematics?
BTW Also my teacher said my answer has no common sense and that I won't be able to do the HSC well if I keep reading questions wrong.