Question

In the expression xy² , the values of both variables x and y are decreased by 20%. By this the value of the expression will be decreased by 

(a) 40% 

(b) 80% 

(c) 48.8% 

(d) 51.2%

Answer 1

(c) 48.8%

New value of x = \(\frac{80}{100}\)x = 0.8x

New value of y² = \(\frac{80}{100}\)y x \(\frac{80}{100}\)y = 0.64y²

^{\(\therefore\)} New value of expression = 0.8x x 0.64y²

= 0.512 xy²

^{\(\therefore\)} % reduction in the value = \(\frac{Xy-0.512Xy^2}{Xy^2}\)x 100%

= (0.488 × 100)% = 48.8%