To solve this problem, we need to find the percentage of correctly answered questions out of the total.

Step-by-step Solution:

1. Total questions: 120
2. Questions answered correctly: 78
3. Calculate the percentage:

$\text{Percentage} = \left( \frac{\text{Correct Answers}}{\text{Total Questions}} \right) \times 100$

$\text{Percentage} = \left( \frac{78}{120} \right) \times 100 = 65\%$

So, the student worked 65% of the problems correctly.

Would you like a detailed explanation or have any questions?

Related Questions:

1. If the student answered 90 questions correctly, what would be the percentage?
2. What percentage would it be if the student answered 60 out of 120 correctly?
3. If the test had 150 questions and the student got 78 right, what is the new percentage?
4. What percentage would be obtained if the student got 78 right out of 200 questions?
5. How many more questions would the student need to answer correctly to reach 80%?

Tip:

When finding percentages, remember to multiply the fraction by 100 to convert it into a percentage value.