it took marty 42 min to write a book report. then he spent 18 min correcting this report. explain how can you use mental math to find how long marty spent on his report?

Round the two numbers.

40 + 20 = ?

60

To find the total time Marty spent on his report, we can use mental math and add the times together.

1. First, we add the time it took Marty to write the book report, which is 42 minutes.
2. Then, we add the time Marty spent correcting the report, which is 18 minutes.
3. To perform the addition, we can break down the calculation mentally:
- First, add the 10s: 40 + 10 = 50
- Next, add the 2s: 2 + 8 = 10
- Finally, add the two sums together: 50 + 10 = 60
4. Therefore, Marty spent a total of 60 minutes on his report.

By using mental math, we were able to quickly find the answer without using a calculator or writing anything down.