posted by John .
1. After each meal, I drew a chart with /on a computer that I had bought by paying a lot of money.
2. I drew the chart on the computer after the meal.
3. With the money, I bought a computer, and I drew spending charts on/with it.
4. I earned some money by selling drinks during the summer vacation. I bought a used / secondhand computer with the money. After the meal, I turned on the computer and drew a spending chart on the notepad.
(Are the sentences all correct? Can we use both 'on' and 'with' before 'a computer'?)
It's better to use "on" with "computer" or "the computer" or "a computer."
The sentences are correct and mean approximately the same thing -- with few differences.
You can use either "used" or "second-hand" to describe the computer in #4.
The visual image of drawing a chart "on the computer" could be confusing. For example, I have "Post It" notes on my computer. I assume that you drew the chart on the monitor screen rather than the computer body. For this reason, although "on" is adequate, I would suggest using "with" since it is the instrument used in making the chart. Example 4 is better at clarifying this.
Since the cost is not related to being able to draw a chart (#1), I would suggest breaking it up into two sentences.
I hope this helps a little more. Thanks for asking.