Arithmetic · real student question

Evaluate (2/5) * (-209/7) + 1041 + 4/5.

Question

Evaluate

25×(2097)+1041+45\frac{2}{5}\times\left(-\frac{209}{7}\right)+1041+\frac{4}{5}

Step-by-step solution

  1. Do the multiplication first (order of operations). Multiply numerators and denominators straight across, keeping the negative sign:

    25×(2097)=41835\frac{2}{5}\times\left(-\frac{209}{7}\right)=-\frac{418}{35}

    Nothing cancels since gcd(2,7)=gcd(209,5)=1\gcd(2,7)=\gcd(209,5)=1.

  2. Group the two fractional terms before touching 1041. Handling 41835+45-\frac{418}{35}+\frac{4}{5} on its own keeps the numbers small. Over the denominator 3535, 45=2835\frac{4}{5}=\frac{28}{35}, so

    41835+2835=39035=787-\frac{418}{35}+\frac{28}{35}=-\frac{390}{35}=-\frac{78}{7}

    (dividing numerator and denominator by 55).

  3. Write the whole number over the same denominator.

    1041=1041×77=728771041=\frac{1041\times 7}{7}=\frac{7287}{7}

  4. Combine into a single fraction.

    72877787=72097\frac{7287}{7}-\frac{78}{7}=\frac{7209}{7}

  5. Check whether it reduces, then convert. 7209=3×2403=32×801=7209=3\times 2403=3^{2}\times 801=\ldots contains no factor 77 (indeed 7×1029=72037\times 1029=7203, remainder 66), so 72097\frac{7209}{7} is already in lowest terms. As a mixed number it is 1029671029\frac{6}{7}, i.e. x1029.857143x\approx 1029.857143.

  6. Estimate as a check. 25×(29.857)11.94\frac{2}{5}\times(-29.857)\approx -11.94, and 11.94+1041+0.81029.86-11.94+1041+0.8\approx 1029.86 ✓, matching the exact value.

Answer

72097=1029671029.857\frac{7209}{7}=1029\frac{6}{7}\approx 1029.857

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