A fully charged cellular phone can work in a standby positions (which means that we do not use it for making phone calls) for 72 hours, or we can talk continuously for 3 hours on it, and then we ahve to recharge it again. This cell phone, after t was fully charged, was in standby position for 27 hours, and the owner conducted a 45-minute conversation, also. How many more minutes could we talk on this phone?
Let B be the fully charged battery capacity.
Talking continuously for 1 hour drains B/3 capacity.
Standby for 1 hour drains B/72 capacity.
The standby has drained 27 * B/72 = 3B/8 capacity.
The conversation drained B/3 * 45/60 = B/4 capacity.
In total, we've drained (3/8 + 1/4) = 5/8 B capacity.
We can talk for 3/8 B more capacity.
How many hours worth is 3/8 B on conversation mode?
B/hr = 3
3B/8hr = 3*3/8 = 9/8 hr.
9/8 hr = 67.5 min