A decimal number has a ,[object Object], that separates the whole part from the decimal part.

• •Whole part: 12
• •Decimal part: 45

[object Object]

• •1: hundreds
• •2: tens
• •3: units
• •[object Object],: decimal point
• 4: tenths (110)
• 5: hundredths (1100)
• 6: thousandths (11000)

[object Object],: Align the decimal points!

[object Object],: 12.5 + 3.25

  12.50
+  3.25
-------
  15.75

1. Multiply without considering decimal points
2. •Count the total number of digits after decimal points
3. •Place the decimal point in the result

[object Object],: 2.5 × 1.2

• 25 × 12 = 300
• 2 digits after decimal points (1+1)
• Result: 3.00 = 3

[object Object],:

• •×10: shift decimal point to the right, ,[object Object],
• •×100: shift 2 positions, ,[object Object],

By a whole number

Perform division normally and place the decimal point in the quotient.

[object Object],: 7.5 ÷ 3 = 2.5

By a decimal

Transform the divisor into a whole number.

[object Object],: 7.5 ÷ 2.5

• Multiply both by 10
• 75 ÷ 25 = 3

[object Object],:

• •÷10: shift decimal point to the left, ,[object Object],
• •÷100: shift 2 positions, ,[object Object],

To the nearest tenth

Look at the hundredths digit

• •If ≥5: round up
• •If <5: keep

[object Object],:

• •3.47 ≈ 3.5
• •3.42 ≈ 3.4

To the nearest unit

Look at the tenths digit

• •3.7 ≈ 4
• •3.2 ≈ 3