1.

The intensity of a sound gets reduced by 20% on passing through two consecutive slabs is :

Answer»

0.4
0.36
0.3
0.6

Solution :Let initial intensity = I.
after passing through one SLAB `I_(1) = I - (20)/(100) I = (4I)/(5)` .
after passing through `2^(nd)` slab
`I_(2) = I_(2) = (4I)/(5) - (20)/(100) ((4I)/(5)) = (16 I)/(25)` .
% decrease in intenity = `(I - I_(2))/(I) xx 100`
= `(I - ((16 I)/(25))/(I) ) xx 100 = 36%`.
HENCE, the correct CHOICE is (b).


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