Question 51
Every 20 minutes during a week an exact amount of litres of water (always the same amount) is transferred from a tank with $25000$ litres to another tank, initially empty. From this second tank, at regular intervals of time, first $1$ litre is withdrawn, then $2$, then $3$, etc. Right at the end of the week the last transfer and the last withdrawal coincide, the second tank being empty at that moment. Determine how much water has been withdrawn in total during the week, if the data of the problem allow it. (Transfers and withdrawals are assumed to be instantaneous. The first transfer is made after the first $20$ minutes and the first withdrawal after the first interval of time.)