Questions

An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons is called an Ion.

Cation:

An ion is a cation (positive ion) if it is created by electron loss and is attracted to the cathode in electrolysis.

Anion:

An ion is an anion (negative ion) if it is created by an electron gain and is attracted to the anode.

The valence of an ion is equal to the number of electrons lost or gained and is indicated by a plus sign for cations and a minus sign for anions.

Ex: Na +, Cl−, Ca ++,...

SDR means Special Drawing Rights.

SDRs are a measure of a country's reserve assets with IMF and, whereas not 'money' in the strict sense, have several characteristics of money as interest-bearing assets, store of value, and means of settling indebtedness.

International financing instrument created in 1970 by the International Monetary Fund (IMF) to coincide with the disfavor of the US dollar as the principal currency of the world trade. Also called paper gold, an SDR is neither paper nor gold but an accounting entry. It is not backed by any currency or precious metal and is used only among governments and IMF for balance Of payments settlements.

First weigh 3 against 3 balls. If the ball contains among these six balls, then take the three balls which weighed over, and weigh the ball 1 against 1. If the balls are not equal and any one of the ball weighs more, that is the overweight ball, else the one among the three which is not weighed is the ball. If the 3 against 3 balls were equal, then weigh the 2 balls, then the overweight ball will be found.

The logic in the given puzzle is 

4 + 4 = 4 * 4+1 = 4 * 5 = 20

5 + 5 = 5 * 5+1 = 5 * 6 = 30

6 + 6 = 6 * 6+1 = 6 * 7 = 42

7 + 7 = 7 * 7+1 = 7 * 8 = 56

Similarly

9 + 9 = 9 * 9+1 = 9 * 10 = 90.