To determine if the pairs of ratios provided form proportions, we need to check if the cross products of each pair are equal.
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For \( \frac{2.25}{10} \) and \( \frac{9}{40} \): \[ 2.25 \times 40 \quad \text{and} \quad 10 \times 9 \] Calculate the cross products: \[ 2.25 \times 40 = 90 \quad \text{and} \quad 10 \times 9 = 90 \] Since \( 90 = 90 \), this pair forms a proportion.
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For \( \frac{2.5}{10} \) and \( \frac{90}{40} \): \[ 2.5 \times 40 \quad \text{and} \quad 10 \times 90 \] Calculate the cross products: \[ 2.5 \times 40 = 100 \quad \text{and} \quad 10 \times 90 = 900 \] Since \( 100 \neq 900 \), this pair does not form a proportion.
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For \( \frac{2.25}{12} \) and \( \frac{90}{40} \): \[ 2.25 \times 40 \quad \text{and} \quad 12 \times 90 \] Calculate the cross products: \[ 2.25 \times 40 = 90 \quad \text{and} \quad 12 \times 90 = 1080 \] Since \( 90 \neq 1080 \), this pair does not form a proportion.
In conclusion, the only set of ratios that form a proportion is \( \frac{2.25}{10} \) and \( \frac{9}{40} \).
Thus, the answer is: Start Fraction 2.25 over 10 End Fraction equals Start Fraction 9 over 40 End Fraction.