A corncob (figure), shaped like a cone, has the radius of its broadest end as 2.1 cm and length (height) as 20 cm. If each 1 cm2 of the surface of the cob carries an average of four grains, find how many grains are there on the entire cob.
Here, ? = cm
cm = 20.11 cm
Therefore, the curved surface area of the corn cob = πr?
cm2 = 132.726 cm2 = 132.73 cm2 (approx)
Number of grains of corn on 1 cm2 of the surface of the corn cob = 4
Therefore, number of grains on the entire curved surface of the cob
= 132.73 × 4 = 530.92 = 531 (approx)
So, there would be approximately 531 grains of corn on the cob.