Speed Calc sans Radar

Algebra Level pending

I was driving to our neighboring city yesterday when I noticed a car overtaking us at a high speed. As soon as the car passed us I started to count out seconds until the car reached a crossroad and continued to count until we reached the same crossroad. If the first count was 17 and the second count was 27 and I maintained a uniform speed of 106 km/hr how fast was the other car going? Assume it also maintained a uniform speed. Give the answer to the nearest km/hr.


The answer is 168.

Guiseppi Butel by Guiseppi Butel , 90, Canada

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3 solutions

1 Helpful 0 Interesting 0 Brilliant 0 Confused
Genis Dude
Feb 6, 2017

Let the both travel 'x' distance.

Speed of our car is 106km/h =((53*5)/9) m/s

Speed =x/time

Therefore,(53*5)/9=x/27

→x=3*265

Speed of their car = x/time

→3*265/17

~168.3

0 Helpful 0 Interesting 0 Brilliant 0 Confused
Guiseppi Butel
Feb 5, 2017

D= r*t

D1 = r1 * t1,

D2 = r2 * t2, but D1 = D2, therefore

r1 * t1 = r2 * t2

or r2 = (r1* t1)/t2

(27*106)/17 = 168

0 Helpful 0 Interesting 0 Brilliant 0 Confused

Can you write a solution that is helpful to those who cannot solve it? Else I'm inclined to delete this solution to encourage others to contribute a relevant answer.

Brilliant Mathematics Staff - 4 years, 4 months ago

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