The intensity of a sound wave gets reduced by 20% on passing through a slab. The reduction in intensity on passage through two such consecutive slabs is

Intensity after passing through one slabI'=I-20100×I=I-I5=4I5So, intensity after passing through two slabsI"=I'20100×I'=4I'5=16I25       ∴          %decrease=I-16I25I×100=36%