maths mc

Let C be the total number of coins

5*(4C/9)+2*(5C/9)=90
20C/9 + 10C/9 =90
30C/9 =90
30C =810
C =27

Therefore,the number of coins in the box is 27

Hope that it helps :)

2007-04-26 13:00:58 補充：
The right answer is C~I forgot to type just now...sorry

$5 : $ 2 = 4 x : 5 x

$ 5 ( 4x ) + $ 2 ( 5x ) = $ 90
20 x + 10 x = 90
30 x = 90
x = 3

so $ 5 = 4 x 3 = 12
$ 2 = 5 x 3 = 15

12 + 15 = 27

the ans. is c

C
let the no. of $5coin be X
the no. of $2coin be5/4X
5(X)+2(5/4X)=90
15X=180
X=12
thus,the total no. of the coins is 12+(5/4)(12)=27

設有x個$5硬幣,有y個$2硬幣

5x+2y=90 - (1)
x/y=4/5 - (2)

由(2)
5x=4y - (3)

代(3)進(1)
6y=90
y=15

代y=15入(3)
5x=60
x=12

所以盒入面有的硬幣
=x+y
=27

答案:C

Let x & y be the number of $5 & $2 coins respectively.
(1) x:y=4:5 => x = 4y / 5
(2) 5x+2y=90

5x + 2y = 90
5 (4y / 5) + 2y = 90
4y + 2y = 90
6y = 90
y = 15

x = 4y / 5
= 4 (15) / 5
= 12

Total number of coins = x + y
= 12 + 15
= 27

Therefore, ans = C.