Solution:

48 minutes.

Donald duck's speed = X km/seconds
pool current speed = Y km/seconds

2/(X+Y) = 40
2/(X-Y) = 60

Solving the simultaneous equations gives X = 1/24

Therefore, to cover 2km will take 2/X = 48 seconds

Solution:

Marshall lives in House no.36
Robin lives in House no.4
Barney lives in House no.9
Lily lives in House no.35
Lyndsy lives in House no.24

Solution:

444 + 444 + 44 + 44 + 4 + 4 + 4 + 4 + 4 + 4 = 1000

Solution:

There are 5 Insect-A, 7 Insect-B & 6 Insect-C.

Let 'A' be the number of Insect-A, 'B' be number of Insect-B and 'C' be number of Insect-C.
A+B+C = 18
8A+6B+6C = 118
2B+C = 20
Solving this, A=5, B=7, C=6

Solution:

24 13 11 5
----------
24 0 0 0
11 13 0 0
6 13 0 5
6 2 11 5
8 0 11 5
8 5 11 0
8 13 3 0
8 8 3 5
8 8 8 0

Solution:

Little Johny have Rupees 99.98 in his wallet when he entered the store.

Solution:

Didn't you say that you sold your well to this farmer?' Birbal asked the neighbour. 'So, the well belongs to him now, but you have kept your water in his well. Is that right? Well, in that case you will have to pay him a rent or take your water out at once.'The neighbour realized that he was outwitted. He quickly apologized and gave up his claim."

Solution:

9+8+7+65+4+3+2+1+0

Solution:

The only number is 2592. 2^5 is 32 and 9^2 is 81. 32*81 is 2592.

Solution:

3:36 PM.
The clock loses 10 minutes each hour,
so it loses 5 minutes every half-hour,
and it loses 1 minute very 6 minutes.

It is 12:50 PM at 1:00 o'clock.
It is 1:40 PM at 2:00 o'clock.
It is 2:30 PM at 3:00 o'clock.
It is 2:55 PM at 3:30 o'clock.
It is 3:00 PM at 3:36 o'clock.