Q.Most commonly used index number is :

The price index number is the most commonly used type of index number.

Index numbers are classified mainly as price, quantity (volume) and value index numbers. Of these, the price index number — which measures the relative change in the price level of a group of commodities between a base period and a current period — is by far the …

Fisher's index satisfies the time reversal test.

The time reversal test requires $P_{01} \times P_{10} = 1$ (ignoring the factor 100). Laspeyre's and Paasche's indices individually fail this test. Fisher's ideal index, being the geometric mean of the two,

$P_{01}^{F} = \sqrt{P_{01}^{L}\times P_{01}^{P}},$

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