Mathematics, 07.07.2019 04:30 glitch14

Dave can complete a sales route by himself in 4 hours. james can do the same job in 5 hours. how long will it take them to do it working together?

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We can solve this problem by calculating the individual rate of working and equate it to their total rate of working.

If Dave can complete a sales route in 4 hours, then his working rate is

$\frac{1}{4}$

Also, if James can do it in 5 hours, then his working rate is

$\frac{1}{5}$

Let

be the hours that both will use to complete the sales route,

Then rate at which both completes this task is
$\frac{1}{x}$

Meaning if we add their individual rates we should get

$\frac{1}{x}$

That is;

$\frac{1}{4} + \frac{1}{5} = \frac{1}{x}$

The LCM is
20x

So let us multiply through with the LCM.

$20x \times \frac{1}{4} + 20x \times \frac{1}{5} =20x \times \frac{1}{x}$

5x + 4x = 20

We simplify to get,

9x = 20

Dividing through by 9 gives;

$x = \frac{20}{9}$

$x = 2\frac{1}{9}$

Therefore the two will complete sales route in
$2 \frac{1}{9}$
hours.

Answer from: Quest

where are the choices?

Answer from: Quest

starting with:

5 + x - 12 = 2x - 7

5 + x - 12 - x = 2x - 7 - x (subtract x from both sides)

5 - 12 = x - 7 (combine and cancel x's from both sides)

5 - 12 + 7 = x - 7 + 7 (add 7 to both sides)

0 = x (add numbers together on both sides)

so in order for the equation to be true, x must be 0.

trying x = -0.5

5 + x - 12 = 2x - 7 (original equation)

5 + -0.5 - 12 = 2(-0.5) - 7 (plug in value of x)

5 + -0.5 - 12 = -1 - 7 (did multiplication)

-7.5 = -8 (did addition on both sides)

since -7.5 is obviously not equal to -8, the value of -0.5 for x is wrong.

trying x = 0

5 + x - 12 = 2x - 7 (original equation)

5 + 0 - 12 = 2(0) - 7 (plug in value of x)

5 + 0 - 12 = 0 - 7 (did multiplication)

-7 = -7 (did addition on both sides)

since -7 equals -7, that demonstrates that the value of 0 for x is correct.

trying x = 1

5 + x - 12 = 2x - 7 (original equation)

5 + 1 - 12 = 2(1) - 7 (plug in value of x)

5 + 1 - 12 = 2 - 7 (did multiplication)

-6 = -5 (did addition on both sides)

since -6 is obviously not equal to -5, the value of 1 for x is wrong.

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