Question

A corn cob shaped somewhat like a cone has a base radius of 2.1 cm and length 20 cm. If each 1 sq. cm of the surface of the cob carries an average of four grains, find approximately how many grains you would find on the entire cob?

• A. 531
• B. 630
• C. 431
• D. 730

Answer 1

The correct option is A

531

Given, radius = 2.1 cm and height = 20 cm

Total number of grains on the corn cob = 4 x Curved surface area of the corn cob

Let the slant height of the corn cob be $l$.
Then, $l=\sqrt{r^2+h^2}$
$=\sqrt{{2.1}^2+{20}^2}$
$=20.11$

Curved surface area $=\pi rl$
$=\frac{22}{7}\times 2.1\times 20.11$
$=132.73c{m}^2$

Total number of grains on the corn cob
$=132.73\times 4=530.92$

Therefore, there would be approximately 531 grains of corn on the cob.