I would look this one up on Google
Answer:
Density of 18.0-karat gold mixture is
.
Explanation:
A mixture of 18 parts gold, 5 parts silver, and 1 part copper.
Let mass of gold be 18x
Let the mass of silver be 5x
Let the mass of copper be 1x
The density of gold = 
The density of silver = 
The density of copper =

Volume of the gold in the mixture = 
Volume of the silver in the mixture = 
Volume of the copper in the mixture = 
Mass of the mixture = M = 18x+5x+1x =24x
Volume of the mixture = 
Density of the mixture:

A- Radio waves, is the answer
Voltage = current x resistance
since R is doubled, current must reduce by half.
So,
new current = 120/2 = 60mA