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7th Class Mathematics Comparing Quantities Question Bank Comparing Quantities

  • question_answer
    A certain sum of money lent out at a certain rate of simple interest per annum, doubles itself in 10 years. In how many years will it triple itself?

    A)  20 years          

    B)  16 years       

    C)  12 years          

    D)  10 years

    Correct Answer: A

    Solution :

    (a)\[{{A}_{1}}=2P=P+\frac{\Pr \,t}{100}\] \[\Rightarrow \]\[P=\frac{P.r.10}{100}\] \[\Rightarrow \]\[r=10\] Again \[{{A}_{2}}=3P=P+\frac{\Pr {{t}_{2}}}{100}\] \[2=\frac{10\times {{t}_{2}}}{100}\] \[\Rightarrow \]\[{{t}_{2}}=20\] 


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