Question

2 cars need 8days to remove sand.

Additional car joined the work from day 4 to to reduce the time.
when will they remove all the sand.

-6 days
-6 1/3 days
-6 1/4 days
-7 1/3 days

please show steps
Thanks in advance.

Answer 1

1 car would need 16 days

so
a car removes 1/16 pile/carday

1/16 pile /carday * 4 days *2 cars
= 1/2 pile in 4 days

so we need
1/16 pile/carday * n days * 3 cars = 1/2 pile

n = 1/2 * 16/3
= 8/3 more days = 2 2/3 more
so
4 + 2 2/3 = 6 2/3