Question

How many ounces of pure nickel must be added to 150 ounces of alloy 70% pure to make an alloy which is 85% pure?

Answer 1

150 oz.

Explanation:

There are already 150 ounces of alloy of nickel.

Of this 150 oz, 70% is pure i.e. nickel content = 150(0.7) = 105 oz

Now available is

Nickel Other metals

105 45

Let x oz of pure nickel is added.

Then new alloy will have 105+x oz nickel in total of 150+x oz.

Percentage pure =
`(105+x)/(150+x) =85%`

Simplify to get

`(105+x)/(150+x) =(85)/(100) \\\\Cross multiply:\\85(150+x) =100(105+x)\\12750+85x =10500+100x\\100x-85x = 12750-10500\\15x = 2250\\x = 150`

Hence answer is 150 oz should be added.