# trouble with thomas calculus $1$ textbook

in thomas calculus $1$ textbook 12th edition, in page $154$ question $26$, it says: ///The number of gallons of water in a tank, t minutes after the tank has started to drain is $Q(t)=200(30-t)^2$How fast is the water running out at the end of $10$ min?// and the solution guide says:

solution textbook

why $t=10$??? end of $10th$ minute is $11th$ minute, right? then why? i'm completely confused and i really need your help guys. thank you. :-*

• is this actually a math question? Nov 18 '16 at 15:15
• this question is in math book, i don't know. you tell me
– user390715
Nov 18 '16 at 15:15
• Oh I thought your question was about end of $10$th minute should be $t=11$ Nov 18 '16 at 15:17
• isn't it math???
– user390715
Nov 18 '16 at 15:23
• It's the same reason why we live in the 21st century even though all our year numbers start with the digits 20: the year 2000 occurred at the end of the 20th century, not the beginning. Nov 18 '16 at 15:51

You start at $t=0$. At the end of the first minute, you are at $t=1$. At the end of the second minute, you are at $t=2$. In general, at the end of $n$ minutes, you are at $t=n$.