To find the fraction of students who scored below 80% on the test, we need to first determine the total fraction of students that scored 90% or better, and those that scored between 80% and 89%.
- Fraction of students scoring 90% or better: \( \frac{1}{3} \)
- Fraction of students scoring between 80% and 89%: \( \frac{2}{5} \)
To find the fraction of students who scored below 80%, we can first add the two fractions together and then subtract from 1 (which represents the whole class).
To add these fractions, we need a common denominator. The least common multiple of 3 and 5 is 15.
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Convert \( \frac{1}{3} \) to a fraction with a denominator of 15: \[ \frac{1}{3} = \frac{5}{15} \]
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Convert \( \frac{2}{5} \) to a fraction with a denominator of 15: \[ \frac{2}{5} = \frac{6}{15} \]
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Add the two fractions together: \[ \frac{5}{15} + \frac{6}{15} = \frac{11}{15} \]
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Subtract the sum from 1 to find the fraction of students who scored below 80%: \[ 1 - \frac{11}{15} = \frac{15}{15} - \frac{11}{15} = \frac{4}{15} \]
Therefore, the fraction of students who scored below 80% on the test is \( \frac{4}{15} \).