Answer: The mom was waiting for half an hour (0.5 hours)
Step-by-step explanation:
They arrived in the mall at the 1:00 hs, and their mother said that she will be back at the 2:30 hs.
the difference between those is:
2:30hs - 1:00hs = 1:30hs
so the gilrs had one hour and 30 minutes to be in the mall. and knowing that 30 minutes is half an hour, we can write this as 1.5 hours.
now, she spended:
5/6 of an hour in the toy store
2/3 of an hour in the pet store
1/2 of an hour in the food court.
then in total we have:
5/6 + 2/3 + 1/2 = 5/6 + (2/2)*(2/3) + (3/3)*(1/2)
5/6 + 4/6 + 3/6 = 12/6 = 2
so the total time is two hours, this means that when they go back to the bench, their mom will be there for:
2hs - 1.5hs = 0.5 hs
half an hour.