Respuesta :
It will be 180 days until they all do laundry on the same day again. I found this by finding the least common multiple of each number.
12 x 15 = 180
10 x 18 = 180
9 x 20 = 180
Hope this helps!
12 x 15 = 180
10 x 18 = 180
9 x 20 = 180
Hope this helps!