SOLUTION: Hi the amount of water in a tank decreases by half every half hour.the tank now has 70 cubic metres of water. How much water will be left after 90min. thanks

Now        70
30 min     35
60 min     17.5
90 min     8.75

The condition says

V(t) = ,

where V(t) is the current volume,  is the initial volume and t is time in hours.


In 1.5 hours,  v(1.5) = 70 : 2^(2*(3/2)) =  = 8.75 cibic meters.




Or, 3/2 hours is 3 times (1/2) of an hour.


So, divide 70 by 2 three times.


You will get the same answer.