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# Maths ( rate and ratio )急..

1.In each of the following, find a : b :c if

(a) a exceeds b by 20% and c is 25%less than a;

(b)a : b = 1 : 5 and c:b = 2 : 3

2.In a test, the marks that three students A,B and C got are in the ratio 3 : 5 : 4.If C got 18 marks less than B ,find

(a)the marks that B gots;

(b) the total marks that A, B and C gots.

3.A piece of work can be completed by x people in 10 days. If 1 more person is added ,the work can be completed in8 days. What is the value of x?

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1.In each of the following, find a : b :c if

(a) a exceeds b by 20% and c is 25%less than a;

a = (1+20%)b (Given)

a:b = 1.2:1 = 6:5 = 12:10

c = (1-25%)a (Given)

c:a = 0.75:1 = 3:4 = 9:12

Hence, a:b:c = 12:10:9

(b)a : b = 1 : 5 and c:b = 2 : 3

a:b = 1:5 (Given)

a:b = 1:5 = 3:15

c:b = 2:3 (Given)

c:b = 2:3 = 10:15

Hence, a:b:c = 3:15:10

2.In a test, the marks that three students A,B and C got are in the ratio 3 : 5 : 4.If C got 18 marks less than B ,find

(a)the marks that B gots;

B:C = 5:4 (Given)

B/C = 5/4

4B = 5C

4B = 5(18) (Given that C = 18)

B = 22.5

Hence, B got 22.5 marks

(b) the total marks that A, B and C got.

A:B:C = 3:5:4 (Given)

Hence, total marks they got

= (18/4)*(3+5+4)

= 54

3.A piece of work can be completed by x people in 10 days. If 1 more person is added ,the work can be completed in8 days. What is the value of x?

A piece of work can be completed by x people in 10 days,

Work needs = 10x

1 more person is added ,the work can be completed in8 days,

Work needs = 8(x+1)

10x = 8(x+1)

10x = 8x+8

2x = 8

x = 4

• 第二題既答案我好似計到90- -

18x[5/(5-4)]

=18x(5/1)

=90

18係B-C得出黎既結果

5係B果個ratio

(5-4)係B-C既ratio

老師教-3-

2009-10-08 20:51:29 補充：

Total mark 我就計到216

18x[(3+5+4)/(5-4)]

=18x(12/1)

=216

18係B-C得出黎既結果

(3+5+4)係個total既ratio

(5-4)係B-C既ratio

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