Question

Someone help please. I don't know how to do number 10.

Answer 1

.25x + .50(1000 - x) = .45(1000)

.25x + 500 - .50x = 450
Combine like terms on the left
-.25x + 500 = 450
Subtract 500 from both sides
-.25x = - 50
Divide both sides by -.25
x = 200
1000 - 200 = 800

Answer 2

Set up two equations
x+y=1000 since the amount of both alloys needs to add up to 1000
(50x+25y)/1000=45 this is the equation for the percent of the new alloy
then combine the two equations and get rid of the y variable which leaves you with .025x=20. so the answer is 800 grams of the 50% metal alloy are used.