Strategies for addition

Maths

There are 2271 satellites currently in space. What is this number rounded to the nearest 10?

There are 2271 satellites currently in space. What is this number rounded to the nearest 100?

The moon Ganymede takes 172 hours to orbit Jupiter. What is this number rounded to the nearest 10?

The moon Ganymede takes 172 hours to orbit Jupiter. What is this number rounded to the nearest 100?

When rounded to the nearest 10, it takes Mars approximately 690 days to orbit the Sun. What is the greatest number of days it can take?

When rounded to the nearest 10, it takes Mars approximately 690 days to orbit the Sun. What is the  least number of days/