Solution:

100/9 (fraction number is also a number)

lets say 'X' is the number.
10/X = X - 10
9X = 100
X = 100/9

Solution:

two hours.

Harish who could paint the wall in 3 hours could paint 2/3 of the wall in just two hours. Ganpat who paint the wall in 6 hours could paint 1/3 of the wall in two hours.
2/3 + 1/3 = 1.

Solution:

Total Number of Matches: 63
Explanation:
32+16+8+4+2+1 = 63

Solution:

4100

some people might guess 5000

Solution:

42857

Let the number be x
10x +1 = 3(100,000 + x)
=> x = 42857.

Solution:

54
x3
===
162

Solution:

3 hours

Explanation :
(1/4 + 1/6 - 1/12) ^ (-1)
= (1/3)^(-1) = 3

Solution:

12

Solution:

117(1+3+5,3+4)

Solution:

10968

Water image is 89601