Chapter R - Section R.1 - Real Numbers - R.1 Assess Your Understanding - Page 16: 30

a.) 25.861 b.) 25.861

Part 'a' of this question is asking for the number 25.86134 to be rounded to three decimal places. First, find the number in the third decimal place. Then look at the number in the fourth decimal place- if the number is 0-4, you can leave the number in the third decimal place as is. If it's 5-9, you have to 'round up' the number in the third decimal by adding 1 to the number. In this case, the number in the third decimal place is 1, and the number in the third decimal place is 3. Since the number in the fourth decimal place is lower than five, you don't have to round up the 1. That makes the answer 25.861. Part 'b' of this question is asking for the number 25.86134 to be truncated at the third decimal point. Truncating just means that you can leave off all the numbers after the number in the indicated decimal place without rounding- like taking a pair of scissors and cutting them off the end. The number in the third decimal place is 1, so leave off everything after the 1 and the answer becomes 25.861.