You buy 80 stamps for 17 dollars some stamps were 15 cents each and the others were 25 cents each. how many of each kind did you buy

30 of the 15 cent stamps and 50 of the 25 cent stamps

Step-by-step explanation:

Create a system of equations, where x is the number of 15 cent stamps and y is the number of 25 cent stamps:

x + y = 80

0.15x + 0.25y = 17

Solve by substitution by rearranging the first equation:

x + y = 80

x = 80 - y

Substitute 80 - y as x into the second equation:

0.15x + 0.25y = 17

0.15(80 - y) + 0.25y = 17

12 - 0.15y + 0.25y = 17

12 + 0.1y = 17

Solve for y:

0.1y = 5

y = 50

Plug in 50 as y into the first equation, and solve for x:

x + y = 80

x + 50 = 80

x = 30

So, you bought 30 of the 15 cent stamps and 50 of the 25 cent stamps

5x + 3y = - 4

step-by-step explanation:

the equation of a line in standard form is

ax + by = c ( a is a positive integer and b, c are integers )

express the line first of all in slope- intercept form

y = mx + c ( m is the slope and c the y-intercept )

to calculate m use the gradient formula

m = ( y₂ - y₁ ) / ( x₂ - x₁ )

with (x₁, y₁ ) = (7, - 3) and (x₂, y₂ ) = (4, - 8)

m = = -

y = - x + c ← is the partial equation

to find c substitute either of the 2 points into the partial equation

using (4, - 8 ), then

- 8 = - + c ⇒ c = -

y = - x - ← in slope-intercept form

multiply all terms by 3 to eliminate the fractions

3y = - 5x - 4 ( add 5x to both sides )

5x + 3y = - 4 ← in standard form