1.60/20 =0.08
0.08 per pen
Step-by-step explanation:

Answer: 20%.
Step-by-step explanation:
Given, The price of a shirt is marked down from $12.50 to $10.00.
Previous price = $12.50
New price = $10.00
Change in price = Previous price - New price
= $12.50 - $10.00
= $2.50
Now, the percent decrease of the shirt = 

Hence, the percent decrease of the shirt = 20%.
There are 5 solutions for this system.
x^2 + 4y^2 = 100 ____1
4y - x^2 = -20 ____2
Add both 1 & 2 together. x^2 gets cancelled
4y^2 + 4y = 80 (send 80 to the other side and divide by 4)
Then equation the becomes : y^2 + y -20 =0
Now factorise the equation: (y+5) (y-4) = 0
Solve for y : y = -5 and y = 4
Using the values of y to find the values of x. From equation 1:
x^2 = 100 - 4y^2 x = /100 - 4y^2 (/ means square root) Replace values of y
y = -5, x = /100 - 4(-5)^2 = /100 - 100 = 0
y = 4, x = /100 - 4(4)^2 = / 100 - 64 = /36 = -6 or 6
Thus we have 6 solutions y = -5, 4 and x = -6, 0, 6