1B Decimal Operations Study Guide

📘 Key Vocabulary

Decimal — a number with a dot (decimal point) that separates the whole number part from the fractional part. (decimal)

Place Value — the value of a digit based on its position in a number. (valor posicional)

Tenths — the first place to the right of the decimal point (0.1). (décimos)

Hundredths — the second place to the right of the decimal point (0.01). (centésimos)

Sum — the answer when you add. (suma)

Difference — the answer when you subtract. (diferencia)

Tens	Ones	.	Tenths	Hundredths
	3	.	4	5
	2	.	7	0

Line up the decimal points, then add zeros to fill empty places.

  3.45
+ 2.70    ← added a zero
------
  6.15

2.5 × 1.3 → 25 × 13 = 325
Total decimal places: 1 + 1 = 2
Answer: 3.25

1 If the divisor has a decimal, move the decimal point right to make it a whole number.
2 Move the decimal point in the dividend the same number of places.
3 Divide as with whole numbers.
4 Place the decimal point in the quotient directly above its position in the dividend.

7.2 ÷ 0.6 → move both 1 place right → 72 ÷ 6 = 12

Adding/Subtracting: Line up decimal points → add zeros → compute

Multiplying: Multiply as whole numbers → count total decimal places → place the point

Dividing: Move decimals to make divisor whole → divide normally

Line up the decimal points, NOT the last digits! This is the most common mistake when adding or subtracting decimals.
Count total decimal places in multiplication. If you forget, your answer will be 10× or 100× too big or too small.
Move the decimal the same number of places in both the divisor and dividend when dividing.
"Sum" means add, "Difference" means subtract. Don't mix them up on word problems!

1. 3.45 + 2.7 = ?

2. 8.3 − 4.56 = ?

3. 2.5 × 1.3 = ?

4. 7.2 ÷ 0.6 = ?