8th Class Mathematics Direct and Inverse Proportions

  • question_answer 20)                 Two persons could fit new windows in a house in 3 days. (i) One of the persons fell ill before the work started. How long would the Job take to now?    (ii) How many persons would be needed to fit the windows in one day?

    Answer:

                    (i) Let the job would take x day.                 We have the following table.

    Number of persons 2 \[2-1=1\]
    Number of days 3 \[x\]
    Clearly, more the number of persons, lesser would be the number of days to do the job. So, the number of persons and number of days vary in inverse proportion. So,            \[2\ \times 3=1\times x\] \[\Rightarrow \]               \[x=6\] Thus, the job would now take 6 days. (ii) Let \[x\] persons be needed. We have the following table.
    Number of days 3 1
    Number of person 2 \[x\]
    Clearly, more the number of persons, lesser would be the number of days to do the job. So, the number of persons and number of days vary in inverse proportion. So,            \[3\times 2=1\times x\] \[\Rightarrow \]               \[x=6\] Thus, 6 persons would be needed.

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