I need to prepare a number of questions for my homework on numbers and fractions. Not being a native English speaker, I'm stuck on constructing a question.
Everyday a student solves questions in the following manner:
1st day: n questions
2nd day: n + ${n\over5}$ questions=k questions
3rd day: k + ${k\over5}$ questions=m questions
4th day: m + ${m\over5}$ questions
The question:
(This is the part I'm stuck)
If on the 4th day she solves 648 questions, how many questions did she solve on the 1st day?
(The answer is 375.)
The question shouldn't involve any unknowns, only the numbers ${1\over5}$ and 648.
A student is solving an unlimited supply of problems.
Each day after the first day, the total number of problems solved increases by an amount equal to $\frac{1}{5}$ of the amount of solved problems from the day before.
If by the fourth day the total number of solved problems is $648$, how many problems were solved on the first day?