Question 987202
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1. When t=0, the tub has not yet started to drain:
{{{V(0)=-15(0)+45}}}
{{{V(0)=45}}}
The total volume of the tub is 45 gallons. 
The tub will be half full when V(t)=(1/2)(45gal)=22.5gal:
{{{V(t)=-15t+45}}}
{{{22.5=-15t+45}}} Subtract 45 from each side.
{{{-22.5=-15t}}} Divide each side by -15.
{{{1.5=t}}}
ANSWER: The tub will be half empty in 1.5 minutes.
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2. Domain: [0,3] 
Since t is time, it is not less than zero. So 0<=t. 
If t>3, the volume is negative so t<=3.
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3. Range: [0,45]
V(t) is volume, cannot be less than zero: 0<+V(t)
At t=0, the tub is full at 45 gallons, so: V(t)<=45 
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4. Kid's tub, t when V(t)=0 is time to drain fully:
{{{V(t) = -15t + 45}}}
{{{0=-15t+45}}}
{{{-45=-15t}}}
{{{3=t}}}
It takes 3 minutes to drain this tub completely.
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For the garden tub when V(t)=0:
{{{V(t)=-20t+50}}}
{{{0=-20t+50}}}
{{{-50=-20t}}}
{{{2.5=t}}}
It takes 2.5 minutes to completely drain the garden tub. 
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ANSWER: The garden tub drains faster.
REASONING: The kid's tub drains 45 gal/3 min=15 gal/min.
The garden tub drains 50 gal/2.5 min=20gal/min.
The garden tub drains more water in less time.