Question 1149901
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Each kilogram of the mixture has 3 parts of grade A; 4 parts of grade B and 5 parts of grade C by mass,

in all, there are  3+4+5 = 12 parts in each kilogram


Hence, each single part is  {{{1/12}}} of kilogram, and each kilogram of the mixture contains 
{{{3/12}}} kg of grade A:  {{{4/12}}} kg of grade B  and  {{{5/12}}} kilogram of grade C.


So, the price of 1 kilogram of the mixture is   {{{120*(3/12)}}} + {{{90*(4/12)}}} + {{{60*(5/12)}}} = 30 + 30 + 25 = 85 sh.


To get profit of 8%, the selling price should be  85*(1+0.08) = 85*1.08 = 91.80 ps for kilogram.


The selling cost of 5 kilograms is then  91.80*5 = 459 ps.
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Solved.