At the given rate of decrease of the rock pile, we can calculate that the rock pile has been decreasing for [tex] 1 \frac{11}{24} \: hours[/tex]
- The rate of decrease per hour = [tex] \frac{2}{5}[/tex]
- Total change in size = [tex] - \frac{7}{12}[/tex]
Number of hours that rock has been decreasing :
- [tex] \frac{total change in size }{rate of decrease }[/tex]
- [tex] \frac{7}{12} \div \frac{2}{5}[/tex]
- [tex] \frac{7}{12} \times \frac{5}{2} = \frac{35}{24} = 1 \frac{11}{24} \: hours[/tex]
Therefore, the rock pile has been decreasing for
[tex]1 \frac{11}{24} \: hours[/tex]
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