Multiply both sides of the second equation by 100 to get rid of the decimals:
0.05<em>n</em> + 0.10<em>d</em> = 1.50
==> 5<em>n</em> + 10<em>d</em> = 150
Multiply both sides of the first equation by -5:
<em>n</em> + <em>d</em> = 21
==> -5<em>n</em> - 5<em>d</em> = -105
Add the two equations together:
(5<em>n</em> + 10<em>d</em>) + (-5<em>n</em> - 5<em>d</em>) = 150 + (-105)
Notice that the terms containing <em>n</em> get eliminated and we can solve for <em>d</em> :
(5<em>n</em> - 5<em>n</em>) + (10<em>d</em> - 5<em>d</em>) = 150 - 105
5<em>d</em> = 45
<em>d</em> = 45/5 = 9
Plug this into either original equation to solve for <em>n</em>. Doing this with the first equation is easiest:
<em>n</em> + 9 = 21
<em>n</em> = 21 - 9 = 12
So Donna used 12 nickels and 9 dimes.
Answer:
Justin could buy up to 8 cookies.
Step-by-step explanation:
7 * 1.25 = 8.75
15 - 8.75 = 6.25
6.25/.75 = 8.3333333
Answer:
cm^2
Step-by-step explanation:
area of an equilateral triangle = 
(s = length of the side)
area = 
area = 
area = cm^2
Answer:
- 5(x - 4)(x + 4)
Step-by-step explanation:
Given
- 5x² + 80 ← factor out - 5 from each term
= - 5(x² - 16) ← x² - 16 is a difference of squares and factors in general as
a² - b² = (a - b)(a + b), thus
x² - 16 = x² - 4² = (x - 4)(x + 4)
Thus
- 5x² + 80 = - 5(x - 4)(x + 4) ← in factored form
