Jason is the culprit . The first letters of the months indicated by the numbers written form the name of the killer.

6 -> [J]une
4 -> [A]pril
9 -> [S]eptember
10 -> [O]ctober and
11 -> [N]ovember

The “truck driver” may be going the wrong way, but what about the truck…?! 🙂

Zero…!

Because I know at least one person who is actually alive today AND has no fingers on his left hand (Number of fingers = 0). 

Thus, 5 * 5 * 5 * …. * 5 * 0 * 5 * 5 * 5* 6 * 5 * …. * 5 = 0.  Hence the answer.

Letter ‘X’ will complete the sequence.

The letters are selected from a standard QWERTY keypad, skipping keys in incremented by 1.

Starting with Q, then skipping one key (W) comes ‘E’, then skipping next 2 keys (R, T) comes Y, skipping next 3 (U, I O) comes ‘P’ and so on.

The puzzle – to be precise, the ‘assumption’ part – needs rephrasing. “only 3 of them lie” means that only 3 of them has a history / habit of lying, but it doesn’t imply that they ALWAYS lie. We have to do the additional bit of assumption to conclude the answer. Otherwise, the information provided is insufficient to reach a conclusion.

The question: “What did I say on my way back?”

Practically, you could have said anything you wanted to. May be, you could have said ‘I should have started a little earlier’ or ‘I should have walked a little faster’ (because the puzzle says you were ‘disappointed’ after going to watch sunrise, which indicates that sun had already risen by the time you reached the bridge) or you could have counted the lamp posts. Just because you followed a certain pattern walking one way, it is not necessary that you should follow the same pattern on the way back.

Well, if you were a robot (or something similar), programmed to say ‘1’ or ‘0’ whenever you pass a lamp post which is ‘On’ or ‘Off’ and your sensors, logic accessories etc, were working  properly, you would have said ‘0000000’, unless, of course, one or more lamps were left ‘on’ due to whatsoever reason.

How about an ‘e’ if not “E”? 🙂

Depends on how you define ‘brother-in-law’ and whether the persons involved has siblings, If ‘brother in law’ means ‘sister’s husband’ only AND my mother doesn’t have any sisters, her brother’s brother-in-law would be my father.
Otherwise: If my mother has at least one sister, my mother’s brother’s brother in law can be the husband of her sister (i.e.,  my mother’s brother in law) also.  Further, if ‘we take the other meaning of ‘brother in law’ (wife’s brother), my mother’s brother’s brother in law can be his wife’s brother.

In both the above cases, is there a single, specific term to address such a relation? No idea…! (In ‘Indian style’, I could call him ‘uncle’, but that won’t be in the correct sense of the word.)

Assuming that all boxes contain the same number of chocolates AND that the No. of chocolates per box is at least 10:

Number the boxes as 1, 2, 3 etc.

From each box,
Take as many chocolates as its number. (i.e., take 1 chocolate from Box No. 1,  2 pieces from Box No. 2, 3 from No. 3 and so on. Total = 55) Now, weigh the selected chocolates together.
If all chocolates were proper, the total weight would have been 1100 g. (55 * 20 g) Since each defective chocolate is 1 g less than the standard, the total weight would be less by as many grams as there are such defective chocolates in the selection. (e.g. if 5 defective chocolates were taken, the total weight would be 1105 g only.)
Since the No. of chocolates taken is equal to the box number, the difference in weight (1100 – actual) would be the number of the box containing the defective ones.

A possible reason is that the man staying in the room might have thought that the stranger was a burglar. Reason for the assumption: Had the stranger actually thought that  it was his room, he could have used his key to open the door instead of knocking. This reason, even though apparently logical, is not satisfactory. This is because, just because the stranger knocked the door doesn’t necessarily mean that he’s an intruder. His justification is perfectly logical if he was staying in the  hotel with a companion and he had gone out leaving his companion in the room. In that case, what he would have done upon return is to knock only, because he doesn’t have the key, and there is a person inside who can open the door for him.