Solution:
Assuming 6 legs for each insect, 19 insects will have 114 legs.
But, there are 128 − 114 = 14 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 14 extra legs belong to 7 spiders.
Alternative Solution through Equations:
Let
s be the number of spiders and
f be the number of flies. Then,
s +
f = 19; and
8
s + 6
f = 128.
On solving the above two equations, we get
8
s + 6 (19 −
s) = 128; or
2
s = 128 − (6 × 19).
Thus,
s = 7.
Food for thought:
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