Mental puzzles - can you solve them?!

[Juz]

Dear Admins, can we make this a sticky like joke of the day perhaps?


Puzzle 1:



EGGTIMER A farmer was due to deliver two truckloads of eggs to the supermarket. He wanted the trucks to arrive at exactly 11am.



If the trucks travelled at 30mph they would reach the supermarket at 10am - an hour early. At 20mph they would arrive at noon - an hour late.
How fast should the trucks travel to arrive at 11am?


Juz

[Conor]

OK, I'll bite......24mph?

[Juz]

Correct. Most people say 25.

And your working out please Conor?


Juz

[Conor]

2 hour difference between trucks with 10 mph speed difference = 40 mile difference at 10am

For the trucks to have built up that difference they must have been on the road 4 hours (4 times the 10mile difference). So the 30 mph truck travelled 4 hours to the destination meaning the journey was 120miles. This means they left at 6am (which can be confirmed by 6 hours at 30 mph ariving at 12).

Therefore the right speed would cover the 120 miles in 5 hours, therefore 24mph

[Finless]

Even knowing it is the wrong answer I still worked it out at 25 mph!

Given that a diff of 10mph = a time diff of 2 hours .......

Well come on ..... I'm too thick and already bored ....... and bad tempered 'cause I can't work it out!

[EDIT]FM, he's SO smart the answer was given BEFORE I'd even asked the question!!!!

[Juz]

Well Done Conor!

Juz

[Conor]

Originally Posted by Finless

[EDIT]FM, he's SO smart the answer was given BEFORE I'd even asked the question!!!!

Lol, nah mate, just type faster

[Lynne]

Originally Posted by Juz

Well Done Conor!

Juz

Does he get a gold star for getting it right?

[Juz]

Puzzle 2



Crossing the bridge.

"U2" has a concert that starts in 17 minutes and they must all cross a bridge to get there. All four men begin on the same side of the bridge.You must help them across to the other side. It is night. There is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either 1 or 2 people, must have the flashlight with them. The flashlight must be walked back and forth, it cannot be thrown etc.

Each band member walks at a different speed. A pair must walk together at the rate of the slower man's pace:

Bono:- 1 minute to cross
Edge:- 2 minutes to cross
Adam:- 5 minutes to cross
Larry:-10 minutes to cross

For example: if Bono and Larry walk across first, 10 minutes have elapsed when they get to the other side of the bridge. If Larry then returns with the flashlight, a total of 20 minutes have passed and you have failed the mission.

Juz

[greekbird]

there are two rooms.
one room has 3 switches. the other room has a lamp
the two rooms are separated with a one way door (no gaps or keyholes in the door!)
you have to find which switch lights the lamp.

you are in the first room, you can stay there as long as you like and you can play with the switches as much as you like (this does not mean you can rip them off the wall!)

once you leave the first room to go into the next, you cannot return into the first room.

how do you work out which switch turns the lamp on?