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

  • question_answer x and y vary in inverse proportion. When x is 12, y is 3. Which of the following is not a possible pair of corresponding values of x and y?       

    A)  4 and 9          

    B)         10 and 3.6     

    C)  72 and 0.5     

    D)         5 and 6          

    Correct Answer: D

    Solution :

    For inverse proportion, \[xy=constant\] or \[{{x}_{1}}{{y}_{1}}={{x}_{2}}{{y}_{2}}\] [a] As, \[{{x}_{1}}{{y}_{1}}=12\times 3=36\] \[{{x}_{2}}{{y}_{2}}=4\times 9=36\] \[\therefore {{x}_{1}}{{y}_{1}}={{x}_{2}}{{y}_{2}}\] [b] As, \[{{x}_{1}}{{y}_{1}}=36;{{x}_{2}}{{y}_{2}}=10\times 3.6=36\] \[\therefore {{x}_{1}}{{y}_{1}}={{x}_{2}}{{y}_{2}}\] [c] As, \[{{x}_{1}}{{y}_{1}}=36;{{x}_{2}}{{y}_{2}}=72\times 0.5=36\] [d] As, \[{{x}_{1}}{{y}_{1}}=36;{{x}_{2}}{{y}_{2}}=5\times 6=30\] \[\therefore \]\[{{x}_{1}}{{y}_{1}}\ne {{x}_{2}}{{y}_{2}}\]


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