We an recoganise a person just by listening his voice and without seeing him.HOw ?

Why we see a rainbow just after rains?

We wish to select 6 persons from 8, but if the person A is chosen, then B must be chosen. In how many ways can the selection be made ?

On 1st January every year, a person buys National saving certificates of value exceeding of his last year’s purchase by Rs. 100. After 10 years he finds that the total value of the certificates' purchased by him is $5000. Find the value of certificates purchased by him :-in the first year .

On 1st January every year, a person buys National saving certificates of value exceeding of his last year’s purchase by Rs. 100. After 10 years he finds that the total value of the certificates' purchased by him is $5000. Find the value of certificates purchased by him :- in the 9th year.

In a city no two persons have identical set of teeth and there is no peson without a tooth. Also no person has more than 32 teeth. If we disguard the shape and size of tooth and consider only the positioning of the teeth, the maximum population of the city is

Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it.How much work is done in just holding it? (Take g=10ms^(-2)).

In your neighbourhood a person was appearing weak. His family members asked you the possible reason. You advised him to consult doctor which appear to be some metabolic disorder. Mention any two metabolic disorders.