我觉得应该是25percent fall in quantity demanded,不知道我这样做对不对?
%change in Income= change in income/average income=(25000-15000)/[(25000+15000)/2]=0.5
因为income elasticity 没有变,所以%change in quantity demand 和%change in Income 是成反比的,
所以qantity demanded要fall, =0.5*0.5=0.25