# How many grams of copper should be mixed with 63 grams of zinc to form an alloy containing 55% zinc and 45% copper?

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`m_("Zn")=63"g"`

`p_("Zn")=55`

To calculate percentage of zinc in an alloy of mass `m` you would use the following formula

` ` `p_("Zn")=m_("Zn")/m cdot 100` **(1)**

But we don't know the mass of alloy, but we do know that it contains `63"g"` of zinc and unknown mass of copper. So we have `m=m_("Zn")+m_("Cu")=63+m_("Cu")` so let's put that into (1)

`55=63/(63+m_("Cu"))cdot100`

`55(63+m_("Cu"))=6300`

`63+m_("Cu")=1260/11`

`m_("Cu")=567/11 "g" approx 51.545455 "g"`