If a roommate pays $270 in rent and saves to buy a house, how much does he save each month?

To determine how much the roommate saves each month towards buying a house, we need to look at the information provided. If the roommate pays $270 in rent, that amount essentially represents their monthly housing expense.

Savings typically means the amount set aside after essential expenses are paid. In this scenario, if we consider that the roommate is budgeting their finances and is allocating a specific portion of their income or budget towards savings while still covering their rent, it implies that they are saving part of what they have remaining after expenses.

Assuming the person aims to save a specific amount monthly, the most plausible figure from the choices given is $90. This amount would indicate that after paying rent, the roommate can set aside this figure as savings, suggesting they are careful with their overall budget.

The other figures presented ($270, $730, and $810) either equal or exceed the rent payment, which would be unrealistic for monthly savings unless the roommate had an exceptionally high income or was receiving other funding. Thus, $90 reflects a reasonable and practical figure for monthly savings after accounting for the rent payment.