Escalator

Mary and John have both completed a trip up an escalator.

The speed and number of steps on the escalator is set.

So the time the escalator takes is also set - assuming no steps

Let there be x steps in 1 trip.

John took 15 steps on the way up and took 12 seconds to reach the top.

$\frac{x-15}{12}$   steps per sec

Mary took only 7 steps and took 18 seconds to reach the top. How many steps does the escalator have in total?

$\frac{x-7}{18}$      steps per sec

These are equal

$\frac{x-15}{12}=\frac{x-7}{18}\\ 18(x-5)=12(x-7)\\ 3(x-5)=2(x-7)\\ 3x-45=2x-14\\ x=31 steps$

The escalator has 31 steps.

the reasoning for the answer by this melody person is incorect

the real resoning should be,

once you get to solving for x,

Step 1: Cross-multiply.

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x-15/12=x-7/18

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(x−15)*(18)=(x−7)*(12)

18x−270=12x−84

Step 2: Subtract 12x from both sides.

18x−270−12x=12x−84−12x

6x−270=−84

Step 3: Add 270 to both sides.

6x−270+270=−84+270

6x=186

Step 4: Divide both sides by 6.

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6x=‌186

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x=31