Just as precise measurements are necessary in science, it is equally important to be able to make rough estimates of quantities using rudimentary ideas and common estimate is difficult to obtain, try to get an upper bound on the quantity ):
(a) the total mass of rain-bearing clouds over India during the Monsoon
(b) the mass of an elephant
(c) the wind speed during a strom
(d) the number of strands of hair on your head
(e) the number of air molecules in your classroom.