Mathematics
Grade6
Easy

Question

Amra can type 400 words per hour. To finish writing a report containing 2000 words, she takes ________ hours.

  1. 5
  2. 3
  3. 2
  4. 7

Hint:

In the question posed, we are given the number of words Amra types in an hour. It is 400. We have to find the time required by Amra to finish the report of 2000 words. From the first data, we can find out the rate at which Amra is typing. Using this value, we can find the required quantity.

The correct answer is: 5


    Amra types 400 words per hour
    We have to find the rate at which Amra types. We will find it by taking the ratio of the number of words and the time required to type. As the rate is constant, we will use this value to find the number of hours required to type 2000 words.
    So the equation becomes
    R a t e space equals fraction numerator N u m b e r space o f space w o r d s over denominator T i m e end fraction
space space space space space space space space space equals space fraction numerator 400 over denominator 1 space h o u r end fraction
space space space space space space space space space equals space 400 space w o r d s space p e r space h o u r
    So the rate = 400 words per hour.
    Let’s find the time required to type 2000 words.
    R a t e space equals space fraction numerator N u m b e r space o f space w o r d s over denominator T i m e end fraction
    We will rearrange this equation for time .
    For this, we will multiply both sides by time and divide by rate.
    T i m e space equals space fraction numerator N o space o f space w o r d s over denominator R a t e end fraction
S u b s t i t u t i n g space t h e space v a l u e s space w e space g e t comma
T i m e space equals space 2000 over 400
space space space space space space space space space space space space equals 5 space h o u r s
    Therefore, time required by Amra to type 2000 words is 5 hours.

    We have to be careful about the units. We have to make sure that same quantities have same unit.

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