Estimate the number of hairs on an average human head.

Solution

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If an average person looks at the hair on the face in a mirror, we find that there are about 15 hairs per cm.

So, per cm square would be 15 * 15 = 225 hairs per cm square.

Now, If an average person takes their hand to cover their scalp, it will probably cover it 5 or 6 times (2 for top, 2 for back, 1 for left & 1 for right).

If an average person looks at their hand, the area will probably be 8 cm * 15 cm = 120 cm square. Let’s put all this together to get 120 * 6 * 225 ~ 160,000 hairs.

An average human head has about 160,000 hairs!