Algebra - 3 pencils, 2 pencils and 3 pens, and1 pen

by Fred
(Saxaphaw)

If 3 pencils cost \$.72, and 2 pencils and 3 pens cost \$.78, how much is 1 pen?

Comments for Algebra - 3 pencils, 2 pencils and 3 pens, and1 pen

 Jun 24, 2012 Calculate Cost of Pen by: Staff The answer: x = cost of one pencil y = cost of one pen 3 pencils cost \$.72 3x = \$.72 2 pencils and 3 pens cost \$.78 2x + 3y = \$0.78 Solve for x using the 1st equation 3x = \$.72 3x / 3 = \$.72 / 3 x * (3 / 3) = \$.72 / 3 x * (1) = \$.72 / 3 x = \$.72 / 3 x = \$ 0.24 Substitute 0.24 for x in the 2nd equation, and then solve for y: 2x + 3y = \$0.78 2 * (0.24) + 3y = 0.78 0.48 + 3y = 0.78 0.48 + 3y - 0.48 = 0.78 - 0.48 0.48 - 0.48 + 3y = 0.78 - 0.48 0 + 3y = 0.78 - 0.48 3y = 0.78 - 0.48 3y = 0.30 3y / 3 = 0.30 / 3 y * (3 / 3) = 0.30 / 3 y * (1) = 0.30 / 3 y = 0.30 / 3 y = 0.10 >>> the final answer: The cost of one pen = \$0.10 --------------------------------------- Check the answer by substituting the values of x and y into the original equations: x = \$ 0.24 y = \$0.10 3x = \$.72 3 * (0.24) = .72 .72 = .72, OK 2x + 3y = \$0.78 2 * 0.24 + 3 * 0.10 = 0.78 0.78 = 0.78, OK Thanks for writing. Staff www.solving-math-problems.com