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Spiders on the Web

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"Dad, where had you been?" asked Peter.

"I had been to the attic, my son," replied Dad. "And do you know what I saw there? There was a big web with 15 spiders and flies on it."

"How many spiders were there?" asked the little boy with curiosity.

"Well, there were a total of 96 legs on the web," answered Dad with a smile. "Now you can find out how many spiders were there by yourself. Can't you?"

Can you help the little boy find out how many spiders were on the web in the attic?

Answer: 3


Assuming 6 legs for each insect, 15 insects will have 90 legs.
But, there are 96 − 90 = 6 extra legs.

It is important to note that spiders have 8 legs and flies have 6 legs. So, there are 2 extra legs per spider on the web.
Thus, the 6 extra legs belong to 3 spiders.

Alternative Solution through Equations:

Let s be the number of spiders and f be the number of flies. Then,

s + f = 15; and
8s + 6f = 96.

On solving the above two equations, we get

8s + 6 (15 − s) = 96; or
2s = 96 − (6 × 15).
Thus, s = 3.

Food for thought:

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