Number and Place Value Rounding Numbers to Decimal

Number and Place Value Rounding Numbers to Decimal Places

Learning Objective • To round numbers to a given number of decimal places. Success Criteria • To recall the key rounding rules. • To apply the key rounding rules to round any number to the nearest whole number, tenth, hundredth or thousandth. • To apply understanding to problem-solving questions.

Rounding Rules There are two key rounding rules, which you need to remember. If the deciding digit is < 5, we round down. If the deciding digit is ≥ 5, we round up.

Decimal Places 1. What do we mean by decimal places? Decimal places refer to the position of the digits to the right of a decimal point. 2. What is meant by 1 decimal place? When we say that a number has one decimal place, we mean that it has one digit to the right of the decimal point. 3. How about 2 decimal places or 3 decimal places? When we say that a number has two decimal places, we mean that it has two digits to the right of the decimal point. When we say that a number has three decimal places, we mean that it has three digits to the right of the decimal point.

Rounding to 1 Decimal Place Round 8. 24 to 1 decimal place. units tenths hundredths 8 2 4 Ask yourself: is the deciding digit < or ≥ 5? Step 1: Identify the column where you are being asked to round. We are being asked to round to 1 decimal place so place your finger on the tenths column. Step 2: Now look at the digit and column to the right of 2 - the hundredths column. The hundredths digit is < 5, so we must round down. 8. 24 rounded to 1 d. p. is 8. 2

Rounding to 1 Decimal Place Round 4. 99 to 1 decimal place. units tenths hundredths 4 9 9 Ask yourself: is the deciding digit < or ≥ 5? Step 1: Identify the column where you are being asked to round. We are being asked to round to 1 decimal place so place your finger on the tenths column. Step 2: Now look at the digit and column to the right - the hundredths column. The hundredths digit is ≥ 5, so we must round up. However, the digit in the tenths column is 9, which means that our answer will be 5. 0 4. 99 rounded to 1 d. p. is 5. 0

Rounding to 2 Decimal Places Round 9. 487 to 2 decimal places. units tenths hundredths thousandths 9 4 8 7 Ask yourself: is the deciding digit < or ≥ 5? Step 1: Identify the column where you are being asked to round. We are being asked to round to 2 decimal places so place your finger on the hundredths column. Step 2: Now look at the digit and column to the right of 8 - the thousandths column. The thousandths digit is ≥ 5, so we must round up. 9. 487 rounded to 2 d. p. is 9. 49

Rounding to 3 Decimal Places Round 5. 8432 to 3 decimal places. units tenths hundreds thousandths ten thousandths 5 8 4 3 2 Ask yourself: is the deciding digit < or ≥ 5? Step 1: Identify the column where you are being asked to round. We are being asked to round to 3 decimal places so place your finger on the thousandths column. Step 2: Now look at the digit and column to the right of 3 - the ten thousandths column. The ten thousandths digit is < 5, so we must round down. 5. 8432 rounded to 3 d. p. is 5. 843