文字題.........thx

One number is 4 times that of another number.Their sum is 45.What are the numbers？
Let x be the smaller numberand 4x be the large number.
4x+x=45
 5x=45
x=9


In a test,Peter gets 2 marks foreach correct sum and loses 1 mark for each wrong sum.He does 18 sums and obtains 24 marks.How many collect sums does he get？
Let x be the number of Peter got correct inthe test.
2x-1(18-x) =24
2x-18+x=24
3x=42
 x=42/3
 x=14


A boy divides 60 marbles into two groups so that 7 times the smaller group is equal to 3 times the larger group.What is the number of marbles in the larger group？
Let x be the number of marbles in the larger group and (3x/7) be the number of marbles in the smaller group.
x+(3x/7)=60
7x+3x=60x7
10x=420
x=42

1)
Let x be the smaller number, y be the larger number.
4x = y ---(1)
x+y = 45----(2)

Sub (1) into (2),
x+4x = 45
x = 9

Sub x = 9 into (1),
4 * 9 = y
y = 36

Therefore, the numbers are 9 and 36.

2)
Let x be the number of correct sum, y be the number of wrong sum
x+y = 18 ---(1)
2x-y = 24 ---(2)

(1) + (2),
3x = 42
x = 14

Sub x = 14 into (1),
14+y = 18
y = 4

Therefore, Peter gets 14 correct sum and 4 wrong sum.

3)
Let x be the number of the smaller group, y be the number of the larger group
x+y = 60 ---(1)
7x = 3y ---(2)

From (1),
x = 60 - y ---(3)

Sub (3) into (2),
7(60 - y) = 3y
420 - 7y = 3y
420 = 10y
y = 42

Sub y = 42 into (3),
x = 60 - 42
x = 18

Therefore, the number of mables in the small group is 18, the number of mables in the large group is 42.

1. Let x and y be the numbers.

x=4y...........(1)
x+y=45.......(2)

Sub (1) into (2),
4y+y=45
5y=45
y=9

and x=4y=4x9=36

Thus, the numbers are 36 and 9.

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2. Let x and y be the no. of correct sums and wrong sums respectively.

x+y=18..........(1)
2x-y=24.........(2)

From (1), y=18-x......(3)

Sub (3) into (2),
2x-(18-x)=24
2x-18+x=24
3x=42
x=12

Thus, he gets 12 correct sums.

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3.Let x and y bet the no. of marbles in the large group and small group respectively.

x+y=60........(1)
7y=3x..........(2)

From (1),
y=60-x........(3)

Sub (3) into (2),
7(60-x)=3x
420-7x=3x
420=10x
x=42

Thus, the no. of marbles in the large group is 42.
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Hope the above helps you.

2006-11-14 20:53:49 補充：
Sorry...for the 2nd question, 3x=42x=14sorry for the typing mistake.

1. Let x and y be the two numbers.

{ x=4y ------- (1)
x+y=45 ---- (2)

sub x=4y into (2)
4y+y=45
y=9

sub y=9 into (1)
x=4(9)
x=36

2. Let x be the no. of sums he gets correctly
2x+(-1)(18-x)=24
2x+(-18+x)=24
3x=42
x=14

3. Let x be the no. of marbles in the large group
3x=7(60-x)
3x=420-7x
10x=420
x=42