Solution:

15

Explanation:
3drink = 30 ....... EquationA
1drink + 2 burger = 20 ....... EquationB
burger + 4 fries = 9 ....... EquationC
burger + fries * drink = ?

From EquationA
drink = 10

From EquationB
burger = (20-10)/2 = 5

From EquationC
fries = (9-5)/4 = 1

Hence
burger + fries * drink = 5 + 1 * 10 = 5 + 10 = 15

Solution:

Read the question carefully again. New Year do falls after Christmas but that happens if two different years. The question is put up against the year 2050 and thus there will be 51 weeks and 2 days in between them as New Year will appear on 1 January 2050 and Christmas will happen on 25 December 2050.

Solution:

2 people

Say 2 helpers are Helper1 & Helper2

Helper1 food Helper2 food McDuck's Food
End of Day 1 : 1 4 4
Now 'A' will head back

End of Day 2 : N/A 2 4
Now 'B' will head back

Now Mr. McDuck have 4 day food :-)

Solution:

Tilt the barrel until the fruit juice barely touches the lip of the barrel. If the bottom of the barrel is visible then it is less than half full.If the barrel bottom is still completely covered by the fruit juice, then it is more than half full.

Solution:

I filled a glass full of water and held it over my head for 20 minutes.

Solution:

The mules is moving in circular path and hence outside legs travels more distance than inner legs.

Solution:

Take 10 number of cards in a new deck and change their face direction. For example- You create a new deck of 10 cards and out of 10, 3 faces up in the new deck. So remaining 7 faces up are in the old deck. But hey! while creating the new deck you reversed the face direction of new cards. So actually the 3 cards which were facing up are actually face down in the new deck while 7 faces up.

Solution:

28 =>1+2+4+7+14

cannot be 1 (as number cannot be included)

Solution:

One Night Stand.

Explanation:
Number 'One' + Knight(chess piece) + st + and(symbol &)

Solution:

For this answer is 3^0, 3^1, 3^2... That is 1,3,9,27,81,243 and 729.

Solution:

16-days

In 15-days, he will climb 15-inch and when he climbs 5 inch more, he will be out of the well :-)