Pedro read 1
2
of a book in the morning, and he read some more at night. By the end of the day, he still had
1
3
of the book left to read. How much of the book did Pedro read at night?

Suppose that sahil knows that 45 people with ages of 18 to 29 voted. without using a calculator, he quickly says then 135 people with ages of 30to 49 voted. is he correct? how might sohil have come up with his answer so quickly?