Lesson · M.4.1
Ratios and proportions
Set up a ratio, build a true proportion, and cross multiply to solve for the missing amount, the way HESI A2 math questions ask for it.
ObjectiveM.4.1Read4 minExam weightRatios, Proportions and Percentages ≈ 12% of Mathematics
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- Write a ratio three ways (fraction, colon, words) without mixing up which number comes first.
- Set up a proportion from a word problem so the two ratios compare the same quantities in the same order.
- Cross multiply and solve for the unknown, including when the unknown sits in the first ratio.
What the lesson concludes
- A ratio compares two quantities in a fixed order; the first number named is always the numerator.
- A proportion is two ratios set equal to each other, and it only works if both ratios compare things in the same order.
- Cross multiplying turns a proportion into one multiplication and one division: multiply the diagonal pair, then divide by the number left over.
- Line up units before you set up the proportion. Mismatched units are the most common source of a wrong answer.
- Check your answer by plugging it back into the original ratio. If it does not reduce to the same value, you made an arithmetic slip somewhere.