A corn cob (see in figure), shaped somewhat like a cone, has the radius of its broadest end as 2.1 cm and length as 20cm. If each `1\ c m^2` of the surface of the cob carries an average of four grains, find how many grains you would find on the entire cob?

Explanation

To solve the problem step by step, we need to find the total number of grains on the corn cob based on its surface area and the average number of grains per square centimeter.

### Step 1: Identify the given values
- Radius (r) of the broadest end of the corn cob = 2.1 cm
- Length (h) of the corn cob = 20 cm
- Average number of grains per square centimeter = 4 grains

### Step 2: Calculate the slant height (l) of the cone
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