.
Another way to solve the problem is THIS :
Let "d" be the distance from the epicenter of the earthquake to the station, in kilometers.
Then the "time" equation is
- = 40 seconds.
To solve it, multiply both sides by 15. You will get
5d - 3d = 40*15
2d = 600
d = 600/2 = 300 kilometers. ANSWER
Solved.
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The lesson to learn from my post is THIS :
Learn on how to write the "time" equation
and how to solve it.
The benefit of this approach is in that the equation from the very beginning is written for the unknown value (distance)
and does not introduce an intermediate variable "t" (time).
In school, the traditional method is solving such problems using time.
But a professional way and a method is to write the "time" equation for the unknown distance from the very beginning
and to get the distance from this equation without using the intermediate variable "t".
Ideally when you know and can use EITHER of these two methods.
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See the lesson
- Earthquake waves
int his site with the solution to similar problem.
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By the way, at an interview it is very easy test to distinct a professional solver from an "amateur".
An "amateur" will solve such problem using time.
A professional solver will use the time equation as I explained it above.