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Posted by on Thursday, September 13, 2012 at 4:38am.

The ratio of the number of pupils in Class A to the number of pupils in Class B is 2:5. The ratio of the pupils in Class B to the number of pupils in Class C is 10:3.
a. Find the ratio of the number of pupils in Class A to the number of pupils in Class B to the number of pupils in Class C.
b. If there are 70 pupils in Class A and Class C altogether, how many pupils are there in Class B?
c. If Class B has 40 pupils, how many pupils are there in Class A and Class C altogether?

  • Math Ratios - , Thursday, September 13, 2012 at 10:41am

    A : B = 2 : 5 or 4 : 10 (looking at the next line)
    B : C = 10 : 3

    so A : B : C = 4 : 10 : 3

    b)

    A : C = 10 : 3
    so 3A = 10C ---> A = 10C/3
    also A+C = 70
    12C/3 + C = 70
    12C + 3C = 210
    15C = 210
    C = 14
    B = 56

    c) I assume we go back to the original definition, and the count is different from b)
    A : B : C = 4:10:3
    A:40:C = 4:10:3 = 16:40:12
    Then A 16 , C=12
    A+C = 28

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