### Brain Teasers

# Poor Robot

Jilbert is delighted at her new purchase of a Wheelie Bot (robot). She looks at the box it came in, and reads that it is 'guaranteed to travel 10km on a single battery'. Wow, what a long way! Jilbert puts her Wheelie Bot on a specially designed 1-meter radius circular track, for exercise, and then leaves for the night. The Wheelie Bot starts moving, completing one lap every twenty seconds!

Three hours after Jilbert leaves, her little sister Harriet arrives and sees the new toy. Shrieking with excitement Harriet shouts 'faster, go on, faster'. The Wheelie Bot complies and starts going five times its original speed, zooming around the track again and again - poor Wheelie Bot :( When Jilbert got back and saw her poor Wheelie Bot exhausted she was not a happy sister!

The question is :

How many minutes in total did it take for the Wheelie Bot to run out of batteries?? (please round your answer down to the nearest minute)

Three hours after Jilbert leaves, her little sister Harriet arrives and sees the new toy. Shrieking with excitement Harriet shouts 'faster, go on, faster'. The Wheelie Bot complies and starts going five times its original speed, zooming around the track again and again - poor Wheelie Bot :( When Jilbert got back and saw her poor Wheelie Bot exhausted she was not a happy sister!

The question is :

How many minutes in total did it take for the Wheelie Bot to run out of batteries?? (please round your answer down to the nearest minute)

### Answer

250 minutesHide Answer Show Answer

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## Comments

The answer seems wrong. I get 810 minutes (and 40 seconds, which you

asked to round down). That's 180 minutes at 3 meters/minute, and 630 minutes

at 15 meters per minute: 180*3+630*15 = 9,990 meters, just short of the 10,000

meters guaranteed by the batteries.

asked to round down). That's 180 minutes at 3 meters/minute, and 630 minutes

at 15 meters per minute: 180*3+630*15 = 9,990 meters, just short of the 10,000

meters guaranteed by the batteries.

Oops - I just noticed it's a 1-meter radius track,

not a one meter circumference. That means the robot is

initially doing 18.850 meters per minute,

not 3 as I assumed. So 250 is correct.

not a one meter circumference. That means the robot is

initially doing 18.850 meters per minute,

not 3 as I assumed. So 250 is correct.

"Jilbert" might just be the best female name I've ever come across!

A circular track 1 meter in radius is 2 * pi meters per lap. That is more than 6.28 meters per lap. Now, 10000 / 6.28.... is just under 1592 laps.

At 3 laps per minute, the robot run 530+ minutes. This being a good 9 minutes under 9 hours and Jilbert having left "for the night," it is doubtful she would have gotten back before the battery was exhausted, even without her sister's intervention.

At 3 laps per minute, the robot run 530+ minutes. This being a good 9 minutes under 9 hours and Jilbert having left "for the night," it is doubtful she would have gotten back before the battery was exhausted, even without her sister's intervention.

Stihl is correct! The answer given is wrong. How come this puzzle has been here for 7 years with a wrong answer?

Oops! How did I miss that bit about traveling 5 times as fast? Sorry the answer is correct but a solution explaining eh answer would have been helpful.

After 3 hours robot has gone 3 x 180 = 540 laps.

Distance traveled = 540 x 2 x 3.14159 = 3393

Distance remaining = 10000 - 3393 = 6607 m

Laps remaining = 6607 / (2 x 3.14159) = 1052

@15 laps/min = 1052/15 = 70 min

Total time = 180 + 70 = 250 minutes.

After 3 hours robot has gone 3 x 180 = 540 laps.

Distance traveled = 540 x 2 x 3.14159 = 3393

Distance remaining = 10000 - 3393 = 6607 m

Laps remaining = 6607 / (2 x 3.14159) = 1052

@15 laps/min = 1052/15 = 70 min

Total time = 180 + 70 = 250 minutes.

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