Jan lives \(x\) floors above the ground floor of a highrise building. It takes her 30 seconds per floor to walk down the

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Jan lives \(x\) floors above the ground floor of a highrise building. It takes her 30 seconds per floor to walk down the steps and 2 seconds per floor to ride the elevator. If it takes Jan the same amount of time to walk down the steps to the ground floor as to wait for the elevator for 7 minutes and ride down, then \(x\) equals

A) 4

B) 7

C) 14

D) 15

E) 16

[spoiler]OA=D[/spoiler]

Source: Official Guide
Source: — Problem Solving |

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Vincen wrote:
Mon May 18, 2020 7:01 am
Jan lives \(x\) floors above the ground floor of a highrise building. It takes her 30 seconds per floor to walk down the steps and 2 seconds per floor to ride the elevator. If it takes Jan the same amount of time to walk down the steps to the ground floor as to wait for the elevator for 7 minutes and ride down, then \(x\) equals

A) 4

B) 7

C) 14

D) 15

E) 16

[spoiler]OA=D[/spoiler]

Source: Official Guide
Let's first convert 7 minutes to SECONDS in order to have uniform units of measurement.
7 minutes = 420 seconds

Let's start with a word equation
Jan's travel time (in seconds) WALKING down = Jan's travel time (in seconds) via ELEVATOR + 420 seconds

It takes her 30 seconds per floor to walk down the steps and 2 seconds per floor to ride the elevator.
There are x floors
So, WALKING time (in seconds) = 30x
And ELEVATOR time (in seconds) = 2x

Plug values into word equation to get: 30x = 2x + 420
Subtract 2x from both sides to get: 28x = 420
Solve: x = 420/28
= 60/4
= 15

Answer: D

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Vincen wrote:
Mon May 18, 2020 7:01 am
Jan lives \(x\) floors above the ground floor of a highrise building. It takes her 30 seconds per floor to walk down the steps and 2 seconds per floor to ride the elevator. If it takes Jan the same amount of time to walk down the steps to the ground floor as to wait for the elevator for 7 minutes and ride down, then \(x\) equals

A) 4

B) 7

C) 14

D) 15

E) 16

[spoiler]OA=D[/spoiler]

Source: Official Guide

Since 7 minutes = 420 seconds, we can create the equation:

Jan’s time to walk = Jan’s time to ride

30x = 420 + 2x

28x = 420

x = 15

Answer: D

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