Practice Problems

Answers

  1. We know the 5 students that want an ice cream party equal 20% of the class. We need to find out the total number of students in the class (100%).

    q1-answer

    Since we know that 5 students equal 20% of the class, we can multiply by 5 to see how many students equal 100%.

    Percent 20% \(\stackrel{\times 5}\rightarrow\) 100%
    Students
    		 5 \(\stackrel{\times 5}\rightarrow\) 25

    There are 25 students in the class.

  2. We know that the whole garden‍ (100%) has ‍50 plants. We need to find out how many are vegetables, which are ‍40% of the garden.

    q2-answer

    Because the ‍50 total plants cover all ‍5 of the ‍20% partitions, we first divide ‍50 plants by ‍5 to see that each ‍20% equals ‍10 plants.

    q2-answer

    We then multiply the ‍10 plants by ‍2 to see how many plants equal ‍40%.

    Percent 100% \(\stackrel{\div 5}\rightarrow\) 20% \(\stackrel{\times 2}\rightarrow\) 40%
    Plants 50 \(\stackrel{\div 5}\rightarrow\) 10 \(\stackrel{\times 2}\rightarrow\) 20

    There are ‍20 vegetable plants in the garden.

  3. We know that the entire population of the school ‍(100%) is equal to ‍700 people. We need to find out how many people equal ‍2% of the students.

    We can first divide the population by ‍100 to see how many people equal ‍1% of the students, then multiply by ‍2 to see how many people equal ‍2% of the students.

    Percent 100% \(\stackrel{\div 100}\rightarrow\) 1% \(\stackrel{\times 2}\rightarrow\) 2%
    Students
    		 700 \(\stackrel{\div 100}\rightarrow\) 7 \(\stackrel{\times 2}\rightarrow\) 14

    There are ‍14 students at Hamilton Middle School with red hair.

  4. We know that an entire coin (100%) weighs 25 grams.

    Grams 25 \(\stackrel{\div 25}\rightarrow\) 1 \(\stackrel{\times 16}\rightarrow\) 16
    Percent
    		 100% \(\stackrel{\div 25}\rightarrow\) 4% \(\stackrel{\times 16}\rightarrow\) 64%


    The table shows that we can divide by 25 to figure out that 4% of the coin is represented by 1 gram.

    We know that the coin has 16 grams of copper, so we multiply 4% by 16 to find the percent of the coin represented by the 16 grams of copper.

    64% of the metal in the coin is copper.

  5. We know that the rate of 10 beats per minute is equal to 20% of the normal rate. We need to find out the normal (100%) number of beats per minute a grizzly bear has when not hibernating.

    q5-answer

    Since we already know the value for 20%, we can just multiply by 5 to see how many heart beats equal 100%.

    Percent 20% \(\stackrel{\times 5}\rightarrow\) 100%
    Heart beats
    		 10 \(\stackrel{\times 5}\rightarrow\) 50


    The grizzly bear's usual heart rate is ‍50 beats per minute.

  6. We know that the total number of fossils ‍(100%) is ‍300. We need to find out how many are fossilized snail shells, which are ‍21% of the total.

    We can first divide by ‍100 to see how many fossils ‍1% would be, then multiply by ‍21 to see how many fossilized snail shells 21% equals.

    Percent 100% \(\stackrel{\div 100}\rightarrow\) 1% \(\stackrel{\times 21}\rightarrow\) 21%
    Fossils
    		 300 \(\stackrel{\div 100}\rightarrow\) 3 \(\stackrel{\times 21}\rightarrow\) 63


    There are ‍63 fossilized snail shells in Elmer's collection.

  7. We can think of a group of ‍25 men as the entire amount ‍(100%). We need to find out what percentage of that amount ‍3 men makes.

    Men 25 \(\stackrel{\div 25}\rightarrow\) 1 \(\stackrel{\times 3}\rightarrow\) 3
    Percent
    		 100% \(\stackrel{\div 25}\rightarrow\) 4% \(\stackrel{\times 3}\rightarrow\) 12%

    The table shows that we can divide by ‍25 to find what percentage of the group ‍1 man is.

    Then we multiply by ‍3 to get from ‍1 man to ‍3 men, the number that are left-handed.

    ‍12% of men are left-handed.

Back to '3.7: Value Mixture Problems'