Question

question number 21 and 26

Answer 1

23) suppose he bought x books so 1200/x+10=1200/x-20 or 1200/x+10=1200-20x/x or 1200x=1200x-20xsqure+12000-200x or 20xsqure+200x-12000=0 or xsqure+10x-600=0 or xsqure +30x-20x-600=0 or x(x+30)-20(x+30)=0 or (x+30)(x-20)=0 or x=20