Anonymous
Anonymous asked in 教育與參考其他:教育 · 1 decade ago

中學3年級的數學問題 (有關equation)

有2條不太明白該怎樣寫步驟:

a)Giving that y=3x, if x increase by 5%, find the percentage increase in y.

我知道這條的答案是5,但不知怎樣寫步驟,請大大指點

b)Giving that y=5x*,while *=3, if xdecrease by 20%, find the percentage decrease in y.

這條真的不懂了

Update:

這是初中三的數學,多謝

4 Answers

Rating
  • 1 decade ago
    Favorite Answer

    1.

    y=3x,

    x increase by 5%:

    等號兩端同時乘以1.05

    1.05y= 3(1.05x)

    1.05y-y=0.05y(增加量)

    0.05y / y = 0.05= 5%(增加率)

    Ans: 5%

    2.

    y=5x*,*=3

    所以y=5x^3

    x decrease by 20%:

    5(x-20%x)^3=5(4/5x) ^3=5╳(64/125) x^3=(64/25)x^3

    (64/25)x^3 / 5x^3= 64/125

    所以 (64/125)y=(64/25)x^3

    y-(64/125)y= (61/125)y(減少量)

    (61/125)y/ y =61/125=48.8%(減少率)

    Ans: 48.8%

    (Note: ^3表示 3次方)

    Source(s): 自己
  • 1 decade ago

    你的題目是不是.....

    a)當y=3x時,如果將x放大5%倍,y要放大幾倍?

    3x=y → x=1/3y

    105/100x=35/100y

    405/100x=105/100y

    Ans:5倍

    b)當y=3x*,而*=3次方時,如果將x縮小20%倍,y要縮小幾倍?

    y=5xxx

    ?y=5×4/5x×4/5x×4/5x

    ?y=64/25xxx

    ?=64/125

    Ans:64/125倍

    2006-07-29 13:38:14 補充:

    b)當y=3x*,而*=3次方時,如果將x縮小20%倍,y要縮小幾倍?題目更正y=5x*補充:初三應該知道xxx=x的三次方吧~?因為沒有三次方的數字~所以換成xxx如果要把64/125換成百分率為51.2%

    2006-07-29 13:49:39 補充:

    *更正64/125y=64/25xxx【縮小幾倍】是1-64/125=61/125所以第二題答案應該是61/125百分率則是48.8%剛剛送出才看到前一位人的..檢查後發現自己漏掉【縮小】其字...

    2006-07-29 13:49:46 補充:

    *更正64/125y=64/25xxx【縮小幾倍】是1-64/125=61/125所以第二題答案應該是61/125百分率則是48.8%剛剛送出才看到前一位人的..檢查後發現自己漏掉【縮小】其字...

    Source(s): yy
  • 1 decade ago

    y=5x*是什麼意思?

    x符號是表示乘以,還是指變數x?

  • 1 decade ago

    可不可以翻譯成中文阿...

Still have questions? Get your answers by asking now.