When adding decimals, always add the decimal parts first, then add the whole numbers.

Adding decimals with one decimal place

Example: $1.7 + 2.6 = ?$

1. Add the tenths: $7 + 6 = 13$
   Write 3 in the tenths place and carry 1 to the ones.
2. Add the whole numbers: $1 + 2 + 1 = 4$

$1.7 + 2.6 = 4.3$

Adding decimals with two decimal places

Example: $7.98 + 2.65 = ?$

1. Add the hundredths: $8 + 5 = 13$
   Write 3 and carry 1 to the tenths.
2. Add the tenths: $9 + 6 + 1 = 16$
   Write 6 and carry 1 to the ones.
3. Add the whole numbers: $7 + 2 + 1 = 10$

$7.98 + 2.65 = 10.63$

Important tip

Always line up the decimal points vertically before adding. This keeps the place values in the correct columns.

When subtracting decimals, subtract the decimal parts first, then subtract the whole numbers.

Subtracting decimals with one decimal place

Example: $5.3 - 3.2 = ?$

1. Subtract the tenths: $3 - 2 = 1$
2. Subtract the whole numbers: $5 - 3 = 2$

$5.3 - 3.2 = 2.1$

Subtracting with borrowing

Example: $26.5 - 18.6 = ?$

1. We cannot subtract 6 from 5 in the tenths, so borrow 1 from the ones:
   The 6 becomes 5, and the 5 in tenths becomes 15.
2. Subtract tenths: $15 - 6 = 9$
3. Subtract ones: $15 - 8 = 7$ (we added the borrowed 10 to the 5)
4. Subtract tens: $2 - 1 = 1$

$26.5 - 18.6 = 7.9$

Subtracting decimals with two decimal places

Example: $12.464 - 8.642 = ?$

Line up the decimal points and subtract each column:

  12.464
−  8.642
--------
   3.822

$12.464 - 8.642 = 3.822$

• Step 1: Write the numbers vertically, keeping decimal points in a straight line.
• Step 2: Add or subtract the decimal part (tenths, hundredths, thousandths).
• Step 3: If the result is 10 or more, carry to the next column.
• Step 4: Add or subtract the whole number part.
• Step 5: Put the decimal point in your answer directly below the others.

At the market, Mama Mwajuma bought 2.75 kg of rice and 1.25 kg of beans. To find the total weight, she adds the decimals:

$2.75 + 1.25 = 4.00 \text{ kg}$

She carried home 4 kilograms of food. Decimals help Tanzanian shoppers and sellers measure exact amounts when buying and selling goods by weight.