Question 982426
The total amount of metal in that jewel amounts to
{{{5*(18g)=90g}}} .
{{{"90%"=90/100=0.9}}} , so the {{{0.9}}} of the rings in the jewel is gold.
The total amount of gold in that jewel amounts to
{{{5*(18g)*0.9=81g}}} .
If that {{{81g}}} is going to be {{{"7.5%"=7.5/100=0.075}}} of a new total amount {{{x}}} , then
{{{0.075x=81g}}}--->{{{x=81g/0.075}}}--->{{{x=1080g}}} .
Obviously the total amount of metal added was
{{{1080g-90g=990g}}} , and all that was added silver,
so the amount of silver he could add is {{{highlight(990g)}}} .