Answer :
The ratio of 15 days to a week is 15 : 7.
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Explanation :
Ratio of 15 days to a week :
[tex] \sf : \implies 15 \: days : 1 \: week = \dfrac{15 \: days}{1 \: week}[/tex]
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Now, we know that 1 week has 7 days.
[tex] \sf : \implies 15 \: days : 1 \: week = \dfrac{15 \: \cancel{days}}{7 \: \cancel{days}}[/tex]
[tex] \sf : \implies 15 \: days : 1 \: week = \dfrac{15}{7}[/tex]
[tex] \sf : \implies 15 \: days : 1 \: week = 15 : 7[/tex]
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Hence, The ratio of 15 days to a week is 15 : 7.
