Denise answered 20 questions in a survey. She took 3 min for each of the first 10 questions and twice as long for each of the remaining questions. She started her survey at 1.20 p.m. At what time did she complete her survey?

1. Calculate the time taken for the first 10 questions

Time for first 10 questions = $10 \times 3 = 30$ min

2. Calculate the time taken for the remaining 10 questions

Time per remaining question = $3 \times 2 = 6$ min
Time for remaining 10 questions = $10 \times 6 = 60$ min

3. Calculate the total time taken

Total time = $30 + 60 = 90$ min = 1 h 30 min

4. Determine the completion time

Start time = 1.20 p.m.
Completion time = 1.20 p.m. + 1 h 30 min = 2.50 p.m.