SOLUTION: Mrs. Rivera’s business is gown rental and sale. She decided one day that she would display her 10 newest gowns in her shop’s window to attract customers. If she only had 5 mannequi

The number of displays is 

(10 gowns Choose 5) = 10C5 = 252 displays

Since she changes every two days, 

the last day she will display set #1 will be day #2
the last day she will display set #2 will be day #4
the last day she will display set #3 will be day #6.

So the last day on which she will display a set is twice 
the number of the set.

So the last day on which she will display set #252 will be 
day #504.

So on day #505 she must use a set she has used before.

So the answer is either 504 days or 505 days, depending on what 
is meant by "running out".  Does she "run out" on the last day 
she displays the last set, or on the next day when she can't 
make a new set?  You'll have to ask your teacher whether it's 
504 days or 505 days.

Edwin