8th Class Mathematics Direct and Inverse Proportions Question Bank Direct and Inverse Proportions

  • question_answer If x varies directly as \[{{y}^{2}}\] and \[x=4\] when\[y=5\], then find x when y is 15.

    A)  4                    

    B)         9        

    C)  12                  

    D)         36      

    Correct Answer: D

    Solution :

    \[\frac{x}{{{y}^{2}}}=\frac{4}{{{(5)}^{2}}}=\frac{{{x}_{1}}}{{{(15)}^{2}}}(\because x\,\,\text{varies}\,\,\text{directly)}\] Or \[{{x}_{1}}=\frac{15\times 15\times 4}{5\times 5}\Rightarrow {{x}_{1}}=36\]


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