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24 February, 07:56

Solve with substitutiion: r + 2s = 30 and 2r - s = - 45

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  1. 24 February, 08:46
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    When you substitute, you should solve one equation for a variable. I'll solve the first equation for r.

    r + 2s = 30 Subtract 2s from both sides

    r = - 2s + 30

    Now, substitute the r-value into the second equation and solve for s.

    2r - s = - 45 Substitute in the r-value

    2 (-2s + 30) - s = - 45 Use the distributive property

    -4s + 60 - s = - 45 Combine like terms

    -5s + 60 = - 45 Subtract 60 from both sides

    -5s = - 105 Divide both sides by - 5

    s = 21

    Now, plug the s-value into the first equation.

    r + 2s = 30 Substitute in the s-value

    r + 2 (21) = 30 Multiply

    r + 42 = 30 Subtract 42 from both sides

    r = - 12

    So, s = 21 and r = - 12.
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