Please close your laptops and turn off and put away your cell phones, and get out your note-taking materials. Today’s daily homework quiz will be given at the end of class.
This week’s schedule: • Today: Lecture on Section 4.5A • HW 4.5A: 16 word problems, due tomorrow • Tomorrow: Lecture on Section 4.5B • 16 more word problems due Wed. (HW 4.5B) • Wednesday: Review for Test 2 • Practice Test 2 due Thursday • Thursday:Take Test 2 (125 points) Next week’s schedule: Spring Break!!
Steps in Solving Problems Involving Systems of Two Linear Equations in Two Variables: • Understand the problem. • Read and reread the problem. • Choose two variables to represent the two unknowns. • Translate the problem into two equations. • Solve the system of equations. • Interpret the results. • Check proposed solution in the problem. • State your conclusion. • Check proposed solution in the problem !!!!!
Example One number is 4 more than twice the second number. Their total is 25. Find the numbers. 1. UNDERSTAND Read and reread the problem. Since we are looking for two numbers, we let x = first number y = second number continued
One number is 4 more than twice the second number. continued 2. TRANSLATE x = 2y + 4 Their total is 25. x + y = 25 continued
continued 3. SOLVE We are solving the system x = 2y +4 x + y = 25 Using the substitution method, we substitute the solution for x from the first equation into the second equation. x + y = 25 (2y +4) + y = 25 Replace x with 4 + 2y. 3y + 4 = 25 Simplify. 3y = 21 Subtract 4 from both sides. y = 7 Divide both sides by 3. continued
continued Now we substitute 7 for y into the first equation. x= 4 + 2y= 4 + 2(7) = 4 + 14 = 18 4. INTERPRET Check:Substitute x = 18 and y = 7 into both of the equations. First equation: x = 4 + 2y 18 = 4 + 2(7) True Second equation: x + y = 25 18 + 7 = 25 True State: The two numbers are 18 and 7.
Example Hilton University Drama club sold 311 tickets for a play. Student tickets cost 50 cents each; non-student tickets cost $1.50. If the total receipts were $385.50, find how many tickets of each type were sold. 1. UNDERSTAND Read and reread the problem. Since we are looking for two numbers, we let s = the number of student tickets n = the number of non-student tickets continued
Hilton University Drama club sold 311 tickets for a play. total receipts were $385.50 Admission for students continued 2. TRANSLATE s + n = 311 Admission for non-students Total receipts = + 1.50n 0.50s 385.50 continued
continued 3. SOLVE We are solving the system s + n = 311 0.50s + 1.50n = 385.50 Since the equations are written in standard form (and we might like to get rid of the decimals anyway), we’ll solve by the addition/elimination method. (Substitution could be used instead, if you prefer to do it that way.) Question: If we wanted to eliminate s, what would we multiply the 0.50s in the second equation by to make it become -1s? Answer: Multiply the second equation by –2. s + n = 311 s + n = 311 –s – 3n = –771 –2(0.50s + 1.50n) = –2(385.50) –2n = –460 n = 230 continued
continued Now we substitute 230 for n into the first equation to solve for s. s + n = 311 s + 230 = 311 s = 81 4. INTERPRET Check: Substitute s = 81 and n = 230 into both of the equations. s + n = 311First Equation 81+ 230 = 311 True 0.50s + 1.50n = 385.50Second Equation 0.50(81) + 1.50(230) = 385.50 40.50 + 345 = 385.50 True State: There were 81 student tickets and 230 non student tickets sold.
How could we set this problem up using two variables? How would you check these answers? x = ? Ounces of 16% solution y = ? Ounces of 8 % solution Equation 1? x + y = 32 Equation 2? 0.16 ● x + 0.08 ● y = 0.11●32
You may now OPEN your LAPTOPS and begin working on the homework assignment until it’s time to take the quiz on HW 4.3. The assignment on this material (HW 4.5A) Is due at the start of the next class session.
You will have access to the online calculator on your laptop during this quiz. No other calculator may be used. Please open Quiz 4.3. • IMPORTANT NOTE: If you have time left after you finish the problems on this quiz, use it to check your answers before you submit the quiz! • Remember to turn in your answer sheetto the TA when the quiz time is up.