Answer:
First, look at the second digit in each number. Since 8 is higher than 5, we round 28 up to 30. Since 3 is lower than 5, we leave 53 as it is.
1) 30 + 53 = 83
So, 28 + 53 is approximately 83 when rounded to the nearest 10.
2) 60 + 30 = 90
70 + 50 = 120
40 + 40 = 80
70 - 20 = 50
50 - 50 = 0
50 - 20 = 30
20 - 10 = 10
90 + 10 = 100
90 + 90 = 180