Question 1136050
Traffic signals at each intersection on a main road all change on the same 2 minute cycle. A taxi driver knows that it is exactly 3.5km from one intersection to the next. Without breaking the 50km/hr speed limit, what is the highest average speed, in kilometers per hour, he can travel to get to each intersection as it just changes to green?
<pre>Let the time it takes to get to each intersection be T
Then we get: {{{matrix(4,1, 50 > 3.5/T, 50T > 3.5, T > 3.5/50, T > .07)}}}
.07 minutes = {{{matrix(1,8, (7/100) * 60, "=", (7/5) * 3, "=", 21/5, "=", 4.2, minutes)}}}
Therefore, T > 4.2 minutes
With T being > 4.2, and the light changing in INTERVALS of 2 minutes, then the time he needs to take to get to each GREEN light = 6 (2 * 3) minutes.
Travelling 3.5 km in 6 minutes, his speed MUST be: {{{highlight_green(matrix(1,8, 3.5/(6/60), "=", 3.5/(1/10), "=", 3.5(10), or, 35, mph))}}}
Tutor @IKLEYN is correct. The other person is WRONG!
Why don't they just leave these problems ALONE, and STOP leading these people ASTRAY? It's not helping when they provide WRONG, RIDICULOUS and/or NONSENSICAL answers.
He even got 2 minutes WRONG! FOR HIS INFORMATION, 2 minutes results in a speed of 105 km/h, EXACTLY, NOT 116+ km/h.