Anonymous
Anonymous asked in 科學及數學數學 · 1 decade ago

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?

2 Answers

Rating
  • 匿名
    Lv 7
    1 decade ago
    Favorite Answer

    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

    Source(s): Hope can help you ~
  • 1 decade ago

    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

    唔知岩唔岩

    畀你參考下=)

Still have questions? Get your answers by asking now.