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Rational Numbers Test - 28

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Rational Numbers Test - 28
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  • Question 1
    1 / -0
    Find $$3$$ rational numbers between $$0$$ and $$1$$.
    Solution
    The mean of $$0 $$ and $$ 1$$ is $$\cfrac{0+1}{2}=\cfrac{1}{2}$$.

    The mean of $$0 $$ and $$ \cfrac{1}{2}$$ is $$\begin{pmatrix}0+\cfrac{1}{2}\end{pmatrix}\div2=\cfrac{1}{2}\div2=\cfrac{1}{2}\times\cfrac{1}{2}=\cfrac{1}{4}$$

    The mean of $$\cfrac{1}{2} $$ and $$ 1$$ is $$\begin{pmatrix}\cfrac{1}{2}+1\end{pmatrix}\div2$$

    $$=\begin{pmatrix}\cfrac{1+2}{2}\end{pmatrix}\div2=\cfrac{3}{2}\div2=\cfrac{3}{2}\times\cfrac{1}{2}=\cfrac{3}{4}$$.

    So, the $$3$$ rational numbers between $$0 $$ and $$ 1$$ are $$\cfrac{1}{2},\,\cfrac{1}{4} $$ and $$ \cfrac{3}{4}$$.
  • Question 2
    1 / -0
    Choose the rational number which does not lie between rational numbers $$-\cfrac {2}{5}$$ and $$-\cfrac {1}{5}$$
    Solution
    Since the given rational numbers $$-\dfrac {2}{5}$$ and $$-\dfrac {1}{5}$$ are negative rational numbers, therefore, none of the positive rational number can lie between them.

    Hence, the rational number $$\dfrac {3}{10}$$ does not lie between the rational numbers $$-\dfrac {2}{5}$$ and $$-\dfrac {1}{5}$$ 
  • Question 3
    1 / -0
    If $$D$$ be subset of the set of all rational  numbers, then $$D$$ is closed under the binary operations of ..............
    Solution

    Rational numbers are closed under all these operations except for division. Add two rational numbers, get a rational number; multiply two rationals, get a rational, etc. Problem with division is that if we divide any number by '0' we cannot tell the output. Some people says it is infinity but that's not true. Division by '0' is not defined.

    So correct answer will be option C

  • Question 4
    1 / -0
    Find five rational numbers between $$\displaystyle\frac{-3}{2}$$ and $$\displaystyle\frac{5}{3}$$.
    Solution
    Converting the given rational numbers with the same denominators 
    $$\cfrac{-3}{2}=\cfrac{-3\times3}{2\times3}=\cfrac{-9}{6}$$ and $$\cfrac{5}{3}=\cfrac{5\times2}{3\times2}=\cfrac{10}{6}$$

    We know that $$-9\,<\,-8\,<\,-7\,<\,-6\,<\,\dots\,<\,0\,<\,1\,<\,2\,<\,8\,<\,9\,<\,10$$
    $$\Rightarrow\cfrac{-9}{6}\,<\,\cfrac{-8}{6}\,<\,\cfrac{-7}{6}\,<\,\cfrac{-6}{6}\,<\,\dots\,<\,\cfrac{0}{6}\,<\,\cfrac{1}{6}\,<\,\cfrac{2}{6}\,<\,\dots\,<\,\cfrac{8}{6}\,<\,\cfrac{9}{6}\,<\,\cfrac{10}{6}$$.

    Thus, we have the following five rational numbers between $$\cfrac{-3}{2}$$ and $$\cfrac{5}{3}$$ 
    $$\Rightarrow \cfrac{-8}{6},\,\cfrac{-7}{6},\,\cfrac{0}{6},\,\cfrac{1}{6}and\cfrac{2}{6}$$
  • Question 5
    1 / -0
    Find $$9$$ rational numbers between $$-\displaystyle\frac{1}{9}\;and\;\displaystyle\frac{1}{5}$$.
    Solution
    Convert the rational numbers into equivalent rational numbers with the same denominator.

    LCM of $$9$$ and $$5$$ is $$45$$.

    $$-\displaystyle\frac{1}{9}=\displaystyle\frac{-1\times5}{9\times5}=\displaystyle\frac{-5}{45}$$ and $$\displaystyle\frac{1}{5}=\displaystyle\frac{1\times9}{5\times9}=\displaystyle\frac{9}{45}$$

    The integers between $$-5$$ and $$9$$ are
    $$-4,\,-3,\,-2,\,-1,\,0,\,1,\,2,\,3,\,4,\,5,\,6,\,7,\,8$$.

    The corresponding rational numbers are $$\displaystyle\frac{-4}{45},\,\displaystyle\frac{-3}{45},\,\displaystyle\frac{-2}{45},\,\displaystyle\frac{-1}{45},\,\displaystyle\frac{0}{45},\,\displaystyle\frac{1}{45},\,\displaystyle\frac{2}{45},\,\displaystyle\frac{3}{45},\,\displaystyle\frac{4}{45},\,\displaystyle\frac{5}{45},\,\displaystyle\frac{6}{45},\,\displaystyle\frac{7}{45},\,\displaystyle\frac{8}{45}$$

    On selecting any $$9$$ of them, we get $$9$$ rational numbers between $$-\displaystyle\frac{1}{9}$$ and $$\displaystyle\frac{1}{5}$$ as

    $$\displaystyle\frac{-4}{45},\,\displaystyle\frac{-3}{45},\,\displaystyle\frac{-2}{45},\,\displaystyle\frac{-1}{45},\,\displaystyle\frac{2}{45},\,\displaystyle\frac{3}{45},\,\displaystyle\frac{4}{45},\,\displaystyle\frac{5}{45},\,\displaystyle\frac{8}{45}$$
  • Question 6
    1 / -0
    Write any $$10$$ rational numbers between $$0\;and\;2$$.
    Solution
    Let us write $$0$$ as $$\dfrac{0}{10}$$ and $$2$$ as $$\dfrac{20}{10}.$$


    So, ten rational numbers between these will be,
    $$\dfrac{1}{10},\;\dfrac{2}{10},\;\dfrac{3}{10},\;\dfrac{4}{10},\;\dfrac{5}{10},\;\dfrac{6}{10},\;\dfrac{7}{10},\ \dfrac{8}{10},\ \dfrac{9}{10},\; 1$$

    Hence, option $$D$$ is correct.
  • Question 7
    1 / -0
    For rational numbers $$\dfrac {a}{b}$$ and $$\dfrac {p}{q}$$, where $$a, b, p, q\in Q$$ and .............. condition exists, then they are closed under division.
    Solution
    The numbers $$a\div 0$$ and $$p\div 0$$ are not rational numbers. So, for any rational numbers of the forms $$\dfrac {a}{b}$$ and $$\dfrac {p}{q}$$ where $$b\neq 0$$ and $$q\neq 0$$ and $$a, b, p, q$$ are rational numbers, they are closed under division.
  • Question 8
    1 / -0
    Simplify using associative property :
    $$\dfrac {7}{16} \times \left (\dfrac {-24}{49} \times \dfrac {28}{15}\right )$$
    Solution
    $$\dfrac {7}{16} \times \left (\dfrac {-24}{49} \times \dfrac {28}{15}\right ) = \left (\dfrac {7}{16}\times \dfrac {-24}{49}\right ) \times \dfrac {28}{15}$$ (associative property)

    $$= \left (\dfrac {1}{2} \times \dfrac {-3}{7}\right )\times \dfrac {28}{15}$$

    $$= \dfrac {-3}{14} \times \dfrac {28}{15}$$

    $$= \dfrac {-2}{5}$$
  • Question 9
    1 / -0
    Simplify using associative property :
    $$\dfrac {-8}{9}\times \left (\dfrac {27}{32} \times \dfrac {-8}{21}\right )$$
    Solution
    $$\dfrac {-8}{9}\times \left (\dfrac {27}{32} \times \dfrac {-8}{21}\right ) = \left (\dfrac {-8}{9} \times \dfrac {27}{32}\right ) \times \dfrac {-8}{21}$$ ($$\because$$ associative property)
    $$= \left (\dfrac {-3}{4}\right ) \times \dfrac {-8}{21}$$
    $$= \dfrac {+2}{7}$$
  • Question 10
    1 / -0
    Choose the rational number which does not lie between rational numbers $$\displaystyle-\frac{2}{5}$$ and $$\displaystyle-\frac{1}{5}$$
    Solution

    Consider given the rational numbers$$-\dfrac{2}{5}$$ and $$-\dfrac{1}{5}$$

    Now, given both rational numbers are negative numbers so the number which lies between them will be negative.

    So,$$\dfrac{3}{10}$$ will not lie between them,

    Hence, this is the answer.

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