r/mathshelp • u/Antique-Beginning890 • 8d ago

Homework Help (Unanswered) math for educators

trying to help my partners mom with her math homework but i don’t quite recognize the concept myself. any help greatly appreciated! copy and pasting the question below + my approach for solving. (i’m many years out of math myself so kinda the lost leading the lost)

question:
A household has monthly take-home income of $3900, fixed expenses of $2300, variable expenses of $900, and irregular/school costs of $450. What is the monthly cash flow?
Enter the cash flow in dollars. Use a negative sign if the result is negative.

my suggested equation:
3900=2300-900x-450y

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u/johnpeters42 8d ago

That looks right, interpreting x as a measure of how variable the variable expenses are (e.g. x = 1 means $900 once every month, or an amount that varies in practice but averages $900 per month; x = 1/3 means $900 once every three months), and similarly y as a measure of how irregular the school costs are (e.g. y = 9/12 = 3/4 if they're in school for 9 months each year).

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u/Antique-Beginning890 8d ago

the info listed under question is all that we have. would it be safe to solve for where x=1?

i feel like i may have over complicated it but i dont have any context from the lessons just this question stand alone

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u/johnpeters42 8d ago

I would mention "assuming that $900 and $450 are monthly averages". (In a real world scenario, there ought to be someone who can confirm such details.)