Question

The intensity of sound reduces by 20 $\%$ on passing through a glass slab. If sound of intensity 1 is made to cross through two such slabs, then the intensity of emergent sound will be

• A. $36\%$
• B. $64\%$
• C. $40\%$
• D. $80\%$

Answer 1

The correct option is A $36\%$

Let the intensity of sound be $100$ after passing through a slab,

percentage reduce $=20$%amount of intensity reduced$=20$% of $00=20$

remaining intensity $=100-20=80$

percentage reduction $=20$%

amount of intensity reduced $=20$% of $80=16$

remaining intensity $=80-16=64$

total amount of intensity reduced $=100-64=36$

reduction percentage $=\frac{36}{100}\times 100=36$%