boy 發問於 科學及數學數學 · 6 年前

F3 Maths Problems

The table on the right shows the weighs and marks of Peter in three tests. The weighed mean mark of Peter is 68.

(a) Show that 2u+v=200.

(b)Peter found that the marks for Chinese and Mathematics tests are interchanged and the weighed mean mark should be 72. Find u and v.

Subject Weight Mark

English 2 70

Chinese 2 u

Mathematics 1 v

Need Steps,Plz!

2 個解答

評分
  • 土扁
    Lv 7
    6 年前
    最愛解答

    (a)

    The weight mean mark of Peter :

    (70 × 2 + u × 2 + v × 1) / (2 + 2 + 1) = 68

    (140 + 2u + v) / 5 = 68

    140 + 2u + v = 340

    2u + v = 200

    (b)

    Marks for Chinese and Mathematics tests are v and u respectively instead.

    The weight mean mark becomes :

    (70 × 2 + v × 2 + u × 1) / (2 + 2 + 1) = 72

    (140 + 2v + u) / 5 = 72

    140 + u + 2v = 360

    u + 2v = 220

    u = 220 - 2v ...... [1]

    Put [1] into 2u + v = 200 :

    2(220 - 2v) + v = 200

    440 - 4v + v = 200

    3v = 240

    v = 80

    Put v = 80 into [1] :

    u = 220 - 2(80)

    u = 60

    Hence, u = 60, v = 80

    2015-01-02 15:24:32 補充:

    "The table on the right" should be "The table at the bottom".

  • 6 年前

    "The table on the right"???

    Upload your graph to

    http://postimg.org/

    and post the link here.

還有問題嗎?立即提問即可得到解答。