Solution:

6

It takes two hours for one worker to paint one wall.
In six hours therefore one worker can paint 3 rooms, hence you need six painters to paint eighteen rooms

Solution:

6380

2*2-1 3*3-1 =>38
4*4-1 5*5-1 =>1524 and so on

Solution:

Step 1) Pour 1 liter of Water from gallon A to gallon C. Now 4 liter of Water is left in the gallon A and gallon C is full.

Step 2) Pour Water from gallon C to gallon B. Now as soon as gallon B is full , you know there is one liter of Water is in gallon C.

Solution:

Steps
1. Monica go from side A to B for approx 59 minutes
2. Lisa then move back to side A for 2 minutes to fool guard. Now guard will think she is coming to side A.
3. then she again move toward B :-)

Solution:

10%

100 - [ (100-85)+(100-80)+(100-75) +(100-70)]
=100-(15+20+25+30)
=100-90

Solution:

Of course, it is impossible. Into the second room should have gone the 2nd guest, because the 13th guest was waiting in room number 1

Solution:

Professor Frink said: 'I shall be hanged!' If he was lying, he would be hanged. But that's what the Frink was saying. So he speaks the truth. But if he speaks the truth, he would be beheaded, so then he was not speaking the truth. So it is impossible for the judge to determine wether the person speaks the truth or not. So therefore the judge cannot determine the penalty and sets him free.

Solution:

Both would be the same distance from City owlna. (since they are at a same point)

Solution:

Nine (eight sons have same one sister ,so 8+1=9)

Solution:

9^9^9

(its not 999:p)