Answer:
84 ounces of pure gold
Step-by-step explanation:
Jess has 60 ounces of an alloy that is 40% gold. How many ounces of pure gold must be added to this alloy to create a new alloy that is 75% gold?
Pure gold = 100% gold
Let the number of ounces of pure gold = x
Hence, we have the equation
40% × 60 ounces + 100%× x ounces = 75%(60 + x)ounces
= 0.4 × 60 + 1x = 0.75(60 + x)
= 24 + x = 45 + 0.75x
Collect like terms
x - 0.75x = 45 - 24
0.25x = 21
x = 21/0.25
x = 84 ounces
Therefore, we need 84 ounces of pure gold
4/5x-2>3/10*2x
4/5x-2>3/5x (3/10*2=3/5)
-2>-1/5x (subtract the 4/5x)
10<x (divide by -1/5 and change sign)
That is a difference of two square numbers, we can factorize them easily:
<span>0 =-b^2 + 25
b^2 - 25 = 0
(b + 5)(b - 5) = 0</span>
How to solve your problem
x^{2}-21=100
Quadratic formula
Factor
1
Move terms to the left side
x^{2}-21=100
x^{2}-21-100=0
2
Subtract the numbers
x^{2}\textcolor{#C58AF9}{-21}\textcolor{#C58AF9}{-100}=0
x^{2}\textcolor{#C58AF9}{-121}=0
3
Use the quadratic formula
x=\frac{-\textcolor{#F28B82}{b}\pm \sqrt{\textcolor{#F28B82}{b}^{2}-4\textcolor{#C58AF9}{a}\textcolor{#8AB4F8}{c}}}{2\textcolor{#C58AF9}{a}}
Once in standard form, identify a, b, and c from the original equation and plug them into the quadratic formula.
x^{2}-121=0
a=\textcolor{#C58AF9}{1}
b=\textcolor{#F28B82}{0}
c=\textcolor{#8AB4F8}{-121}
x=\frac{-\textcolor{#F28B82}{0}\pm \sqrt{\textcolor{#F28B82}{0}^{2}-4\cdot \textcolor{#C58AF9}{1}(\textcolor{#8AB4F8}{-121})}}{2\cdot \textcolor{#C58AF9}{1}}
4
Simplify
Evaluate the exponent
Multiply the numbers
Add the numbers
Evaluate the square root
Add zero
Multiply the numbers
x=\frac{\pm 22}{2}
5
Separate the equations
To solve for the unknown variable, separate into two equations: one with a plus and the other with a minus.
x=\frac{22}{2}
x=\frac{-22}{2}
6
Solve
Rearrange and isolate the variable to find each solution
x=11
x=-11