Question 1162242
A couple of ways to go about it
Can let copper=x and the other small fractions of x
 or let copper=24x.  The 24x is not magic, but it is small enough and easily divisible by the other percentages with the exception of lead.  I could have made it 120x, then nickel would have been 75x, copper 40x, lead 6x.  I just thought of working with smaller numbers, that is all.
Nickel is 5/8 of that or 15x
Zinc is 1/3 of that or 8x
Lead is 1/20th or it or 1.2x
The total is 48.2x, and it equals 40 1/6=40.166 lb
putting both in fractional form, 48 1/5x=40 1/6x
x=40 1/6/(241/5)=(241/6)*(5/241); the 241 s cancel and x=(5/6) lb.
That makes
lead 1 lb.
zinc 6 2/3 lb
nickel 12 1/2 lb
and copper 20 lb
They add to 40 (1/6) lb.