She took one of the pebbles and threw it away WITHOUT revealing what colour it was. The remaining pebble was obviously black. As per the promise by the lender, he was supposed to put one white and one black pebble in the bag. Being so, AND as the pebble that remained in the bag was black, it must imply that the pebble that the girl picked was white, forcing the lender to forego the money. (Otherwise, he will have to admit to cheating, which he can’t afford.)

Depending on what ‘hidden’ means, there are multiple ‘hidden’ words in the sentence.

1.   ‘ever’ and ‘very’ hidden within ‘Every’,
2. ‘now’ hidden within ‘knows’,
3. ‘hat’ hidden within ‘that’;
4. ‘scan’ hidden within the adjacent words ‘optics‘ and ‘can‘, and
5. ‘bet’ hidden in ‘be tricky’

Happy Birthday to you.

Swim under water

Possible case: Eve was on life support. The elevator stopped because of power failure, which meant the life-support system that kept Eve alive was no longer operational, which, in turn, meant that Eve was dead.

C

She had booked tickets in advance – TWO tickets (for herself and husband) for the outward journey and only ONE ticket (for herself) to return – means that she knew in advance that she would be returning alone – which implies that she had planned her husband’s murder before they embarked on their journey.

29.

The total number of rungs (odd) can be assumed as 2x + 1, on which the fireman was on rung x + 1, with ‘x’ rungs each above and below (as he was on the ‘middle rung’). Then he climbed 6 rungs, taking him to rung x + 7. Then he had to climb down 10 rungs, taking him to rung No. (x – 3). Later, he climbed 18 rungs, taking him to rung No. (x + 15), which is supposed to be the top of the ladder (2x + 1). i.e., x + 15 = 2x + 1 => x = 14; 2x + 1 = 29. 

The fireman was initially on 15th rung, then climbed 6 runs to rung 21, and then climbed down 10 steps to rung 11. Thereafter, he climbed 18 rungs to reach ring 29, reaching the top of the ladder.

Ignoring factors like inflation, depreciation etc., the transactions have a net impact of profit of $50. Total amount spent = 100 + 150 = 250; Total Amount earned = 125 + 175 = 300 . Net profit = Total earnings – Total expense => 300 – 250 = 50.

As the title of the puzzle indicates, it is impossible. Since the distance to be covered in the second part of the journey is the same as that of the first part, you will have to cover that distance in zero time (which is impossible) to get the average speed doubled.