Algebra · real student question

Solve for x: (5x - 7)/2 - (3x + 4)/3 = (x + 5)/6 + 1.

Question

Solve for xx:

5x723x+43=x+56+1\frac{5x-7}{2}-\frac{3x+4}{3}=\frac{x+5}{6}+1

Step-by-step solution

  1. Find the least common denominator of every term. The denominators are 22, 33 and 66 (the 11 on the right counts as 11\tfrac11), so

    LCD=6.\text{LCD}=6.

  2. Multiply every term on both sides by 6. Multiply the whole term, brackets and all — this is where signs get lost otherwise:

    3(5x7)2(3x+4)=(x+5)+6.3(5x-7)-2(3x+4)=(x+5)+6.

    Each fraction has vanished because 6/2=36/2=3, 6/3=26/3=2 and 6/6=16/6=1.

  3. Expand both sides, distributing the minus sign carefully.

    15x216x8=x+11.15x-21-6x-8=x+11.

    The 2-2 multiplies both 3x3x and +4+4, giving 6x8-6x-8.

  4. Collect like terms.

    9x29=x+11  8x=40  x=5.9x-29=x+11\ \Longrightarrow\ 8x=40\ \Longrightarrow\ x=5.

  5. Substitute back into the original equation. Left side:

    257215+43=182193=9193=83.\frac{25-7}{2}-\frac{15+4}{3}=\frac{18}{2}-\frac{19}{3}=9-\frac{19}{3}=\frac{8}{3}.

    Right side:

    5+56+1=106+1=53+1=83.\frac{5+5}{6}+1=\frac{10}{6}+1=\frac{5}{3}+1=\frac{8}{3}.

    Both sides equal 83\tfrac83, so x=5x=5 is correct.

Answer

x=5x=5

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