我想問吓二題maths的列式和答案......

2007-02-17 6:31 pm

1.Given that x+y=39 and x:y=4:9.
(a)For the expression x:y=4:9,express x in terms of y.
(b)Hence,find the values of x and y.

2.The total number of candies got by Leo.Christine and Mandy is480.Christine gets twice as many as Leo,while Mandy gets half as many as Christine.Find the number of candies of them gets.

May you help me?Write the列式和答案!!!

回答 (1)

用戶111485

2007-02-17 6:46 pm

✔ 最佳答案

1(a)
x:y = 4:9
x/y = 4/9
x = 4y/9,,

1(b)
'.' x = 4y/9 ----(1)
.'. Sub (1) into eq. (x+y=39)
x+y=39
(4y/9) + y = 39
(4y/9) + (9y/9) = 39
13y/9 = 39
13y = 351
y = 27
Sub (y=27) into (1)
x = 4y/9
x = 4(27)/9
x = 12,,
.'. x=12 , y=27

2.Let x be the number of candies got by Leo , y be Christine , z be Mandy.
{x+y+z = 480 ---(1)
{2x = y ---(2)
{y/2 = z ---(3)
Sub (2) into (3)
y/2 = z
2x/2 = z
x = z ---(4)
Sub (4) , (2) into (1)
x+y+z=480
x+2x+x=480
4x=480
x=120,,
Sub (x=120) into (4)
z = 120
Sub (x=120) into (2)
2(120) = y
y = 240
.'. x = 120 , y=240 , z=120

參考: ME

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