TAILIEUCHUNG - Math Word Problem Demystified Phần 8

Tham khảo tài liệu 'math word problem demystified phần 8', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LESSON 18 Using Two Equations IMPLEMENTATION Solve the system x y 8 25x iQy i25 Find the value of y in the first equation. Substitute it in the second equation and solve for X. x y 8 X X- y X y 8-x 25x ỈQy ỉ25 25x 10 8-x 125 25x 80 lOx 125 15x 80 125 15x 80-80 125 - 80 15x 45 T51x_45 T5 15 X 3 Find y x y 8 3 y 8 3 3 y 8 3 y 5 Hence there are 3 quarters and 5 dimes. LESSON 18 Using Two Equations EVALUATION Find the values of each and see if their sum is . 3 quarters 3 X 5 dimes 5 X EXAMPLE Bill is 8 years older than his brother. In 3 years Bill will be twice as old as his brother. Find their present ages. SOLUTION GOAL You are being asked to find the present ages of Bill and his brother. STRATEGY Let X Bill s age y his brother s age X 3 Bill s age in 3 years y 3 his brother s age in 3 years Since Bill is 8 years older than his brother the first equation is X y 8 In 3 years Bill will be twice as old as his brother so the second equation is x 3 2 y 3 IMPLEMENTATION Solve the system X J- 8 X 3 2 y 3 LESSON 18 Using Two Equations Substitute the value of X in the second equation and solve for y since X y 8. X 3 2 y 3 y 8 3 2 y 3 y 8 3 2y 6 y 11 2y 6 y y 11 2y - y 6 ll j 6 11 6 y 6 6 5 y Select the first equation let y 5 and solve for X. x r 8 x 5 8 X 13 Hence Bill is 13 years old and his brother is 5 years old. EVALUATION Check the second equation for x 13 and y 5 X 3 2 y 3 13 3 2 5 3 16 2 8 16 16 EXAMPLE A person walked from his home to the football stadium at a rate of 3 miles per hour. After the game he rode the bus back the same way at a rate of 22 miles per hour. If the total trip took 2 hours how far did he walk

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