The rate of increase of bacterial in a certain culture is proportional to the number of bacterial present. If it is found that the number doubled in 5 hours, prove that the bacterial becomes eight times at the end of 15 hours.

The number of bacteria in a certain culture doubles every hour. If there were 30 bacteria present in the culture originally, how many bacteria will be present at the end of 2nd hour, 4th hour and nth hour ?

The population of a certain is known to increase at a rate proportional to the number of people presently living in the country. If after two years the population has doubled, and after three years the population is 20,000 estimates the number of people initially living in the country.

In a Laboratory, the count of bacteria in a certain experiment was increasing at the rate of 2.5% per hour. Find the bacteria at the end of 2 hours if the count was initially 5, 06,000.

The population of a village increases continuously at the rate proportional to the number of its inhabitants present at any time. If the population of the village was 20, 000 in 1999 and 25000 in the year 2004, what will be the population of the village in 2009?

A certain particle carries 2. 5 xx 10 ^(-16) C of static electric charge. Calculate the number of electrons present in it.

A particular substance is being cooled by a stream of cold air (temperature of the air is constant and is 5^(@)C ) where rate of cooling is directly proportional to square of difference of temperature of the substance and the air. If the substance is cooled from 40^(@)C to 30^(@)C in 15 min and temperature after 1 hour is T^(@)C, then find the value of [T]//2, where [.] represents the greatest integer function.

Agreat physicist of this century (RA.M. Dirac) loved playing with numerical values of Fundamental constants of nature. This led him to an interesting observation. Dirac found that from the basic constants of atomic physics (c, e, mass of electron, mass of proton) and the gravitational constant G, he could arrive at a number with the dimension of time. Further, it was a very large number, its magnitude being close to the present estimate on the age of the universe (~15 billion years) . From the table of fundamental constants in this book, try to see if you too can construct this number (or any other interesting number you can think of). If its coincidence with the age of the universe were significant, what would this imply for the constancy of fundamental constants ?

5 people of a locality were asked about the time they spent in a week in doing social work. They told the number of hous as: x,x+3,x+6,x+7,x+4. find the mean number of devoted by first three members. If mean number of hours of 5 persons is 11 hours, what values do we draw from above data?

In a culture, the bacteria count is 1,00,000. The number is increased by 10% in 2 hours. In how many hours will the count reach 2,00,000, if the rate of growth of bacteria is proportional to the number present?