Question

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

• A. 531 grains
• B. 100 grains
• C. 230 grains
• D. 700 grains

Answer 1

Answer: (A)

531 grains

$r=2.1,h=20$

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

$l=\sqrt{r^2+h^2}$

$=\sqrt{{2.1}^2+{20}^2}$

$=20.11$

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.