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A farm rears 9 ducks and cows in his farm. There are 28 legs altogether.How many ducks are there in the farm?

  • Maths -

    d + c = 9
    2d + 4c = 28

    Multiply the top equation by -2 and add. This will give you the number of cows. Find the ducks by substituting into the first equation.

  • Maths -

    let d=number of ducks reared
    c=number of cows reared
    sum of ducks and cows=d+c=9
    sum of their legs=2d+4c=28 since duck has two legs and cow also has 4 legs
    the two equations give
    d+c=9...1
    2d+4c=28...2
    multiply eqn 1 by 2
    2(d+c=9) which gives 4d+4c=18..3
    now 2d+4c=28
    -2d+2c=18
    we have 2c=10
    therefore c=5 put c into eqn..1
    to get d+5=9
    d=4 meaning there are 4 ducks and 5 cows.proof2*4=8legs in all does 4 ducks and 4*5=20 legs in all does 5 cows.

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