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valkas [14]
3 years ago
5

The time needed to paint a fence varies directly with the length of the fence and inversely with the number of painters. If it t

akes seven hours to paint 280 feet of fence with two painters, how long will it take four painters to paint 720 feet of fence?
Mathematics
1 answer:
astraxan [27]3 years ago
5 0

Answer:

It will take 9 hours with 4 painters  to paint 720 feet of  fence.

Step-by-step explanation:

Given that,

The time needed to paint a fence varies directly with the length of the fence

t\propto  l .......(1)

and inversely with the number of painters

t\propto \frac1P.....(2)

Combination of (1) and (2) is

t\propto \frac lP

where t represents time, l represents length of fence, P represents number of painters.

Again we can write the above equation as

\frac{t_1}{t_2}=\frac{\frac{l_1}{l_2}}{\frac{P_1}{P_2}}

\frac{t_1}{t_2}=\frac{l_1P_2}{l_2P_1}

Given that,

It takes 7 hours with 2 painters  to paint 280 feet of fence .

We need to find time to paint 720 feet of fence with 4 painters.

t_1=7  hours, l_1=280 feet, P_1=2,

t_2=? , l_2 = 720 feet, P_2=4

\therefore \frac{7}{t_2}=\frac{280\times 4}{720\times 2}

\Rightarrow \frac{t_2}{7}=\frac{720\times 2}{280\times 4}

\Rightarrow {t_2}}=\frac{720\times 2\times 7}{280\times 4}

\Rightarrow t_2=9

It will take 9 hours to paint 720 feet of  fence with 4 painters.

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