I drink 0.5 of water per day. What expressions will I need to use to find the number of cups of water she drinks in a week?
Answers
Answer: option D.) 0.5 gallons / 1 day × 16 cups / 1 gallon × 7 days / 1 week
Explanation:
The answer is found by doing analyzing the dimensions (units) of the quantities, placing each factor in a way that lead to the cancellation of the dimensions (units) until you reach the desired units.
You want to find an amount whose final (desired) units are number of cups of water per week.
Therefore, you have to change the given volume of water, that is in gallons, to cups, and the given unit of time, that is in days, to weeks.
To do that, you use the conversion factors derived from the equivalences of the units:
16 cups = 1 gallon
division property ⇒ 1 = 16 cups / gallon
1 week = 7 days
division property ⇒ 1 = 7 days / week
The final step is multiply the given amount, 0.5 gallons of water per day, by the conversion factors that wre just built:
0.5 gallon / 1 day = 0.5 gallon / (1 day) × 16 (cups / gallon) × (7 days / week)
When you follow the units in the expression of the right you verify that:
gallon appears first time in the numerator and a second time in the denominator so they cancel one to each other.
day appears first time in the numerator and a second time in the denominator, so they also cancel each other.
the units left are cups / week, which means that you are getting the number of cups of water she drinks in a week
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