Decimals to Thousandths and Decimal Operations
Warm-up
Athletic timing: the 100 m record is 9.58 seconds. A local runner finishes in 10.004 seconds. How much slower? The answer requires decimal subtraction. Estimate first: about 0.4 seconds. Compute: 10.004 - 9.580 = 0.424 seconds. The thousandths digit in 9.580 is a trailing zero: it does not change the value.
Explore
Precision measurement: students measure 5 classroom objects using kitchen scales (to the nearest gram = 3 decimal places in kilograms) and graduated cylinders (to the nearest mL = decimal in litres). Record in decimal notation. Order from smallest to largest. Add two measurements and subtract another.
Consolidate
Practice
Students compare and order 6 sets of decimals to thousandths, convert 4 decimals to simplified fractions, and solve 6 decimal addition/subtraction problems. Exit ticket: add 3.5 + 1.275.
Exit ticket
Students compare and order 6 sets of decimals to thousandths, convert 4 decimals to simplified fractions, and solve 6 decimal addition/subtraction problems. Exit ticket: add 3.5 + 1.275.
Write 4.072 + 1.850 (align decimal points, add trailing zero). Thousandths: 2+0=2. Hundredths: 7+5=12, write 2 carry 1. Tenths: 0+8+1=9. Ones: 4+1=5. Result: 5.922.
0.450 vs. 0.405. Tenths: 4=4. Hundredths: 5 vs. 0. 5>0. So 0.45 > 0.405. More digits does not mean more value.