Algebra · real student question

Solve x - (x*0.8 - 5000)*0.03 = 7232 for x, giving an exact answer.

Question

Solve for xx, giving an exact answer:

x(0.8x5000)0.03=7232x-\left(0.8x-5000\right)\cdot 0.03=7232

Step-by-step solution

  1. Expand the bracket. Distributing 0.030.03 over the two inner terms:

    0.03(0.8x5000)=0.024x1500.03\left(0.8x-5000\right)=0.024x-150

  2. Subtract the whole bracket, flipping both signs.

    x(0.024x150)=x0.024x+150=0.976x+150x-\left(0.024x-150\right)=x-0.024x+150=0.976x+150

    so the equation reads

    0.976x+150=72320.976x+150=7232

  3. Isolate and divide. Subtracting 150150 gives 0.976x=70820.976x=7082, hence

    x=70820.976x=\frac{7082}{0.976}

  4. Convert to an exact fraction rather than rounding. Multiply numerator and denominator by 10001000 and cancel:

    x=7082000976=44262561x=\frac{7082000}{976}=\frac{442625}{61}

    since gcd(7082000,976)=16\gcd(7082000,976)=16. Because 6161 is prime and does not divide 1010, this fraction has a non-terminating decimal expansion, x=7256.1475409836x=7256.1475409836\ldots — unlike the neighbouring problem with 72267226 on the right, which lands exactly on 72507250.

  5. Decide how to report it. Give 44262561\dfrac{442625}{61} when an exact answer is wanted, or x7256.15x\approx 7256.15 to two decimal places for a money-style context.

  6. Check. 0.976×44262561=70820.976\times\dfrac{442625}{61}=7082 exactly, and 7082+150=7232 7082+150=7232\ \checkmark; numerically 7256.1475409836070.03(0.87256.1475409836075000)=7232.0000007256.147540983607-0.03\left(0.8\cdot 7256.147540983607-5000\right)=7232.000000.

Answer

x=442625617256.15x=\frac{442625}{61}\approx 7256.15

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