Arithmetic · real student question

Solve for X: (X − 40.354/14.4) × 3562/3600 = (147.304 × 600 + 40.354 × 1492)/(14.4 × 3600).

Question

Solve for XX:

(X40.35414.4)35623600=147.304600+40.354149214.43600.\left(X-\frac{40.354}{14.4}\right)\cdot\frac{3562}{3600}=\frac{147.304\cdot 600+40.354\cdot 1492}{14.4\cdot 3600}.

Step-by-step solution

  1. Evaluate the two constants on the left.

    40.35414.4=2.8023611111,35623600=0.9894444444\frac{40.354}{14.4}=2.8023611111\ldots,\qquad \frac{3562}{3600}=0.9894444444\ldots

    Both are exact rationals, so keeping them as fractions (4035414400\tfrac{40354}{14400} and 17811800\tfrac{1781}{1800}) rather than truncated decimals avoids error accumulating through the division that follows.

  2. Compute the numerator on the right, carefully.

    147.304×600=88,382.4,40.354×1492=60,208.168.147.304\times 600=88{,}382.4,\qquad 40.354\times 1492=60{,}208.168.

    The second product is the one to double-check: 40.354×1492=40.354×150040.354×8=60,531322.832=60,208.16840.354\times1492=40.354\times1500-40.354\times8=60{,}531-322.832=60{,}208.168. Their sum is

    88,382.4+60,208.168=148,590.568.88{,}382.4+60{,}208.168=148{,}590.568.

  3. Compute the denominator and the right-hand value.

    14.4×3600=51,840,148,590.56851,840=2.866330401214.4\times 3600=51{,}840,\qquad \frac{148{,}590.568}{51{,}840}=2.8663304012\ldots

  4. Undo the multiplication. Divide both sides by 35623600\tfrac{3562}{3600}:

    X2.8023611111=2.86633040120.9894444444=2.8969088839.X-2.8023611111=\frac{2.8663304012}{0.9894444444}=2.8969088839.

  5. Undo the subtraction and state the exact value.

    X=2.8969088839+2.8023611111=5.6992699950.X=2.8969088839+2.8023611111=5.6992699950.

    Carrying the whole computation in exact fractions gives X=73,082,87912,823,200X=\dfrac{73{,}082{,}879}{12{,}823{,}200}, whose decimal expansion is 5.6992699950095.699269995009\ldots — matching the decimal route to ten places. Note that mis-multiplying 40.354×149240.354\times1492 as 60,192.56860{,}192.568 (a common slip) would shift the right-hand side to 2.86530352.8653035 and the answer to 5.69823095.6982309, wrong in the third decimal.

Answer

X=73,082,87912,823,2005.699270X=\frac{73{,}082{,}879}{12{,}823{,}200}\approx 5.699270

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