## Mario’s Racing Grandma

Mario is testing out a new car at the racetrack. His grandmother took it for a mile lap and averaged 30mph. How fast does Mario have to drive in the second lap to average 60mph for the two miles?

90mph is an alluring answer, but it’s impossible. At 90mph the second lap would take 40 seconds. If Grannie’s first lap at 30mph took 2 minutes, traveling 2 miles in 2 minutes and 40 seconds is an average speed of 45mph. Traveling an average speed of 60mph for 2 miles would take 2 minutes and since the grandma’s lap took all of those 2 minutes, even if Mario could break the sound barrier he wouldn’t be able to average 60mph.

Posted in Brain Teasers

8 Comments on "Mario’s Racing Grandma"

Scott says
November 3, 2014 @ 03:15

im soz but where does it say the lap took 2 mins

@Scott It doesn’t, 2 minutes was just a random time I picked to illustrate speeds. It could be any duration you want.

Jasmine says
November 8, 2014 @ 12:55

I don’t get that one either

Chris says
November 19, 2015 @ 03:01

Easy, he just has to use the teleporter.

Chris says
November 19, 2015 @ 03:05

@Dan explained it a little complicated. If you’ve travelled a set speed for a set distance. To bring your average speed up to double in double the distance is impossible because it would need to take no time for the second lap, therefore doubling your speed.

Hafidz says
January 29, 2017 @ 12:19

Info:
Track length (1 lap) = 1 mile

1st Fact : 30mph for 1 mile = 2 minutes (grandma’s timing).
30mph for 60 minutes (1 hour) = 30mph/60 minutes = 0.5 mile every minute.
30mph for 2 minutes = 0.5 mile x 2 minutes = 1 mile (length of track).

2nd Fact : 60mph for 2 miles = 2 minutes (total timing should be).
60mph for 60 minutes (1 hour) = 60mph/60 minutes = 1 mile every minute.
60mph for 2 minutes = 1 mile x 2 minutes = 2 miles (2 laps length).

Superwhiz Maths Person (also neutral as to not offend those who have a complex of themselves and others) says
March 10, 2018 @ 21:15

Once again, it is because parameters are not explained. Let me do so:

Due to the speed being stated at an exact MPH, this brings into bearing a factor for tolerance, which is due to significant figures. As there are none, this brings our parameters of speed to 30MPH = 30MPH +/- 0.5MPH. This is due to rounding up or down before the next speed is considered as the actual speed, namely 31 MPH.

Therefore, we now have a parameter to work with. We need to accomplish our speed within the parameters of what speed the race is normally counted at, and do exactly the same thing with the significant figures, per second, or in this instance, thousandths of a second. This allows us to travel at 3.6 million miles an hour, and only take the place of 1/1000 of a second. That means if we triple that speed, we get 10.8 million miles an hour.

Based on that information, if the car travels at approximately 1/10th of the speed of light for that next lap (or faster), he will be able to average 60MPH for the two laps, even if the lap was exactly on the limit of ticking over to 31MPH for the first lap.

Superwhiz Maths Person (also neutral as to not offend those who have a complex of themselves and others) says
March 10, 2018 @ 21:23

@Scott
The lap length was 1 mile, and the speed was 30MPH. Therefore the two minutes wasn’t an estimation but a measured speed, which gives you the time. It is called the Distance Formula.