Digital SAT · Math · Problem-Solving and Data Analysis. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A ratio compares two quantities, such as 5 to 3. A rate is a ratio of two different units, such as miles per hour or dollars per ounce. A proportion says that two ratios are equal, which lets you find a missing value.
The safest method is to find the amount for one unit first (the unit rate), then multiply. Keep the same quantity in the same position on both sides of a proportion.
To convert units, multiply by a fraction equal to 1, such as (60 minutes)/(1 hour), chosen so the unwanted unit cancels. Write the units at every step. For areas, a length scale factor must be squared; for volumes, cubed.
Averaging two speeds directly for a trip with equal distances. Average speed is total distance ÷ total time, so find the time for each part first.
Answer: 3,375 bottles
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