Final answer:
Oswald is correct and Sarah is not.
We can determine who is correct by evaluating the inequality using both fractions. Oswald is correct because the result is less than the given number, while Sarah is not correct because the result is greater than the given number.
Step-by-step explanation:
Oswald and Sarah's teacher wrote an inequality on the board. Oswald claims that the fraction 4/5 makes the inequality true. Sarah claims that the fraction 5/4 makes the inequality true to the number 1,240. To determine who is correct, we need to evaluate the inequality using both fractions.
The inequality has two sides, let's call them Side A and Side B. We need to substitute 4/5 for Side A and 5/4 for Side B. If Side A is less than Side B, then Oswald is correct. If Side A is greater than Side B, then Sarah is correct. If Side A is equal to Side B, then both Oswald and Sarah are correct.
Let's substitute 4/5 into the inequality and evaluate: Side A = (4/5)*1240 = 992. Since 992 is less than 1240, Oswald is correct. Let's now substitute 5/4 into the inequality and evaluate: Side B = (5/4)*1240 = 1550. Since 1550 is greater than 1240, Sarah is not correct. Therefore, Oswald is correct and Sarah is not.