An alloy of copper and aluminium has 40% copper.  An alloy of copper and zinc and zinc in the ration of 2 : 7.  These two alloys are mixed in such way that in the overall alloy, there is more aluminium than zinc and copper constitute XY of this alloy.  What is the range of values X can take?

32.25% ≤ X ≤ 40%

Alloy 1                           Copper               Aluminium

                                        2x                            3x

Alloy 2                           Copper               Aluminium

                                        2y                            7y
If Aluminium and Zinc have to be equal, 3x = 7y. The simplest case occurs at the LCM, when both Aluminium and Zinc are 21kg.

Alloy 1                           Copper               Aluminium

                                        14                           21

Alloy 2                           Copper               Aluminium

                                        6                           21
Even a gram of alloy 1 above this level would mean that there is more Aluminium than Zinc in the total alloy. So, this table is a limit on the percentages of different metals.

The percentage of Copper in the total alloy would be (14 + 6)* 100/62 = 32.25%

32.25% ≤ X ≤ 40%