Word problem: What fraction of an hour should the piano still be practiced?  Khan Academy  Summary and Q&A
TL;DR
Pedro needs to practice piano for 3/4 of an hour, but he has only practiced for 1/4 of an hour. The fraction he still needs to practice is 1/2.
Questions & Answers
Q: How much time does Pedro need to practice the piano?
Pedro needs to practice for 1/2 an hour, as he has already practiced for 1/4, leaving him with 2/4 or 1/2 remaining.
Q: Can you explain the visual representation of the fractions?
Sure! The whole hour is divided into quarters, and Pedro needs to practice for 3 out of those 4 quarters. He has already practiced for one quarter, leaving him with 2 quarters or 1/2 to practice.
Q: Why is 2/4 the same as 1/2?
2/4 is equivalent to 1/2 because you can divide both the numerator and denominator by 2. When you simplify, 2 divided by 2 is 1, and 4 divided by 2 is 2.
Q: How can we determine the fraction of an hour Pedro needs to practice?
To find the fraction of an hour Pedro needs to practice, we subtract the fraction he has already practiced (1/4) from the total fraction he needs to practice (3/4), resulting in 2/4 or 1/2.
Summary & Key Takeaways

Pedro needs to practice the piano for 3/4 of an hour.

He has already practiced for 1/4 of an hour.

Pedro still needs to practice for 1/2 an hour.