Questions

At least one black can be chosen in two ways from each box:
Now, probability of choosing at least one black ball from first box 

= 1/2 × [ (2C1× 2C1)/4C2 + 2C2/ 4C2 ]= 5/12

Probability of choosing at least one black ball from 2nd box
= 1/2 × [(4C1×12C1)/16C2 + 4C2/ 16C2] = 9/40

Final probability

= 5/12 + 9/40 = (50 + 27)/120 = 77/120

India does not have any lake or sea comparable with the Great Lakes of the united States or the Caspian Sea of the CIS.

Thermal energy is caused by the motion of atoms and molecules in the matter.

1. Thermal energy is an example of kinetic energy, as it is due to the motion of particles, with motion being the key.
2. Thermal energy results in an object or a system having a temperature that can be measured.
3. Thermal energy can be transferred from one object or system to another in the form of heat.

Isthmus of panama and Isthmus of Suez are well known examples

Let the required number be 'X'

Condition 1 :  

$$\begin{gathered} XX = 2X \\ => 2X2 = X \\ => X = 12 \end{gathered}$$

Condition 2 :

$$\begin{gathered} X × X = X2 \\ => X = 12 \end{gathered}$$

Therefore, 12 is the number which becomes double when it is divided by itself and becomes half when it is multiplied by itself.