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Evaluate, (44-28)/(12 x -2) and 8² x -12 - 2496 / -12 x 9 without using mathematical tables or a calculator.

Mathematics

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Answers

2 parts
a

23\frac{2}{3}

b

313\frac{31}{3}

0.3675
11

Step-by-step solution

15 steps

Here are the solutions to the problems:

1. Evaluate:

Part a· 2 steps

44−2812×2\frac{44-28}{12 \times 2}

  1. Evaluate the numerator and the denominator.

    44−2812×2=1624\frac{44-28}{12 \times 2} = \frac{16}{24}
  2. Simplify the fraction.

    1624=2×83×8=23\frac{16}{24} = \frac{2 \times 8}{3 \times 8} = \frac{2}{3}

    The value is 23\boxed{\frac{2}{3}}.

Part b

313\frac{31}{3}

82×12−2496÷12×9\frac{8^2 \times 12 - 24}{96 \div 12 \times 9}

  1. Evaluate the numerator using the order of operations (PEMDAS/BODMAS).

    82×12−24=64×12−24=768−24=7448^2 \times 12 - 24 = 64 \times 12 - 24 = 768 - 24 = 744
  2. Evaluate the denominator using the order of operations.

    96÷12×9=8×9=7296 \div 12 \times 9 = 8 \times 9 = 72
  3. Divide the numerator by the denominator and simplify.

    74472=93×89×8=939=31×33×3=313\frac{744}{72} = \frac{93 \times 8}{9 \times 8} = \frac{93}{9} = \frac{31 \times 3}{3 \times 3} = \frac{31}{3}

    The value is 313\boxed{\frac{31}{3}}.

    2. Use table of logarithms to evaluate: (6.79×0.391log⁡5)−34\left(\frac{6.79 \times 0.391}{\log 5}\right)^{-\frac{3}{4}}
    Let the expression be YY. We need to find log⁡Y\log Y.

    log⁡Y=−34log⁡(6.79×0.391log⁡5)\log Y = -\frac{3}{4} \log \left(\frac{6.79 \times 0.391}{\log 5}\right) log⁡Y=−34(log⁡(6.79×0.391)−log⁡(log⁡5))\log Y = -\frac{3}{4} \left( \log(6.79 \times 0.391) - \log(\log 5) \right) log⁡Y=−34((log⁡6.79+log⁡0.391)−log⁡(log⁡5))\log Y = -\frac{3}{4} \left( (\log 6.79 + \log 0.391) - \log(\log 5) \right)

    Using 4-figure logarithm tables:
    log⁡6.79=0.8319\log 6.79 = 0.8319
    log⁡0.391=1ˉ.5922\log 0.391 = \bar{1}.5922
    log⁡5=0.6990\log 5 = 0.6990

  4. Calculate log⁡(6.79×0.391)\log(6.79 \times 0.391).

    log⁡(6.79×0.391)=log⁡6.79+log⁡0.391=0.8319+1ˉ.5922=0.8319+(−1+0.5922)=0.4241\log(6.79 \times 0.391) = \log 6.79 + \log 0.391 = 0.8319 + \bar{1}.5922 = 0.8319 + (-1 + 0.5922) = 0.4241
  5. Calculate log⁡(log⁡5)\log(\log 5).

    log⁡(log⁡5)=log⁡(0.6990)=1ˉ.8445\log(\log 5) = \log(0.6990) = \bar{1}.8445
  6. Calculate log⁡(6.79×0.391log⁡5)\log \left(\frac{6.79 \times 0.391}{\log 5}\right).

    log⁡(6.79×0.391log⁡5)=0.4241−1ˉ.8445=0.4241−(−1+0.8445)=0.4241+1−0.8445=0.5796\log \left(\frac{6.79 \times 0.391}{\log 5}\right) = 0.4241 - \bar{1}.8445 = 0.4241 - (-1 + 0.8445) = 0.4241 + 1 - 0.8445 = 0.5796
  7. Calculate log⁡Y\log Y.

    log⁡Y=−34×0.5796=−0.75×0.5796=−0.4347\log Y = -\frac{3}{4} \times 0.5796 = -0.75 \times 0.5796 = -0.4347
  8. Convert log⁡Y\log Y to characteristic and mantissa form for antilog.

    −0.4347=−1+0.5653=1ˉ.5653-0.4347 = -1 + 0.5653 = \bar{1}.5653
  9. Find the antilog of 1ˉ.5653\bar{1}.5653.

    Y=antilog(1ˉ.5653)≈0.3675Y = \text{antilog}(\bar{1}.5653) \approx 0.3675

    The value is 0.3675\boxed{0.3675}.

    3. Calculate the number of sides of the polygon.
    Let nn be the number of sides of the polygon.
    The sum of the interior angles of an nn-sided polygon is given by the formula:

    S=(n−2)×180∘S = (n-2) \times 180^\circ

    We are given that two interior angles are 178∘178^\circ and 155∘155^\circ. The remaining (n−2)(n-2) angles each measure 143∘143^\circ.
    So, the sum of the interior angles can also be expressed as:

    S=178∘+155∘+(n−2)×143∘S = 178^\circ + 155^\circ + (n-2) \times 143^\circ
  10. Equate the two expressions for the sum of interior angles.

    (n−2)×180=178+155+(n−2)×143(n-2) \times 180 = 178 + 155 + (n-2) \times 143
  11. Expand and simplify the equation.

    180n−360=333+143n−286180n - 360 = 333 + 143n - 286 180n−360=143n+47180n - 360 = 143n + 47
  12. Collect terms involving nn on one side and constants on the other.

    180n−143n=47+360180n - 143n = 47 + 360 37n=40737n = 407
  13. Solve for nn.

    n=40737n = \frac{407}{37} n=11n = 11

    The number of sides of the polygon is 11\boxed{11}.

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