General
General
Easy

Question

Fanny can solve 5 math exercises in an hour. At the same rate, 25 math exercises take ______ hours.

  1. 6
  2. 9
  3. 5
  4. 7

Hint:

We are given the number of math exercises solved by Fanny in 1 hour. It is 5. We have to find the time taken by Fanny to solve 25 math exercises, given the rate is constant. To solve this question, we will find the rate first. We will find the rate using the first data. And from the rate we will find the required value.

The correct answer is: 5


    The given value of number of exercises is 5 and time required is 1 hour.
    Basically we are given a rate at which Fanny is solving the exercise. It is 5 exercises per hour.
    We have to find time taken by him to solve 25 exercises. We have rate with us and it is constant. So we will use to the time required.
    The equation becomes
    R a t e space equals space fraction numerator N u m b e r space o f space e x e r c i s e s over denominator T i m e end fraction
    We will rearrange the expression for time. We will divide the L.H.S and R.H.S of the above equation by rate and multiply it by time.
    T i m e space equals space fraction numerator N u m b e r space o f space e x e r c i s e s over denominator R a t e end fraction
space space space space space space space space space space equals 25 over 5
space space space space space space space space space space equals 5 space h o u r s
    Therefore, Fanny requires 5 hours to solve 25 math exercises.

    The other method is to take the ratios and directly equate them. As the rate is constant, so the ratios will be constant. So we will consider the quantity we have to find as x and then equate the ratios. It will be a shortcut.

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