數學題!!!方程(答得好好就最佳回答)

Let x be the number of right questions.
y be the number of wrong questions.


5x - 4y = 71--------(1)
.
x + y = 25----------(2)

5 x (2) - (1) :

5x + 5y - 5x + 4 y = 125 - 71
9 y = 54
y = 6

So, he gets 6 wrong

Let x be the number of correct answer and y is the number of wrong answer

Form two equations
5x - 4y = 71 .......... (1)
x + y = 25 ...............(2) → x = 25 - y ..............(3)

Insert (3) into (1)
5 (25 - y) - 4y = 71
125 - 5y - 4y = 71
125 - 9y = 71
-9y = 71 -125
-9y = -54
9y = 54
therefore y = 54 / 9 = 6
小明答錯 6 題

Let A be number of correct questions and B be number of incorrect questions
A + B = 25
A = 25 - B

Sub. B into the equation:
5A - 4B = 71
5(25 - B) - 4B = 71
125 - 5B - 4B = 71
125 - 71 = 9B
54 = 9B
B = 6
Therefore, he had 19 correct questions and 6 incorrect questions

設y為他答對的問題數目.
y*5+[(25-y)*-4]=71
5y-100+4y=71
9y=171
y=19
∴他答錯了25-19=6題

Let X be the number of correct answers
Let Y be the number of wrong answers

Total number of answers=25
X+Y=25
X=25-Y

5X-4Y=71
5(25-Y)-4Y=71
125-5Y-4Y=71
125-71=9Y
54=9Y
Y=6

X=25-Y
X=25-6
X=19

Therefore
Siu ming got 19 questions right and 6 questions wrong. (Answer is 6)

Checking:
5(19)-4(6)=95-24=71 which is same as given by the question

Let x 佢答對幾多 y be 答錯幾多,
x+y = 25 (1) <<<< 佢總共答左25條
5x-4y=71 (2) <<<<佢既得分 答對5分 答錯扣4分 最後佢有 71 分

用聯立方程計
(1)x5
5x+5y=125 (3)
(3)-(2):
9y=54
y=6 <<佢答錯左6條.......

答岩都有得計 ....
Sub y=6 into (1)
x+6 =25
x=21

答岩左 21條

13.5=.=!
我咁計唔知唔知呢!
5*25-71/4
=.=!