Step-by-step method

1. Write the measurements in columns, with the largest unit on the left
2. Add the smallest units first
3. If the sum is 10 or more, convert and carry to the next column
4. Continue adding until all columns are done

Example: Adding Length

Add: 7 km 4 hm + 6 km 6 hm

Step 1: Add the smaller unit (hectometres): 4 hm + 6 hm = 10 hm

Convert: 10 hm = 1 km 0 hm

Write 0 in the hm column, carry 1 to the km column.

Step 2: Add kilometres: 1 + 7 + 6 = 14 km

Answer: 14 km 0 hm (or simply 14 km)

Example: Adding Mass

Add: 4 kg 850 g + 3 kg 350 g

Step 1: Add grams: 850 g + 350 g = 1200 g

Convert: 1000 g = 1 kg, so 1200 g = 1 kg 200 g

Write 200 in the g column, carry 1 to the kg column.

Step 2: Add kilograms: 1 + 4 + 3 = 8 kg

Answer: 8 kg 200 g

Example: Adding Volume

Add: 3 L 600 mL + 4 L 450 mL

Step 1: Add millilitres: 600 mL + 450 mL = 1050 mL

Convert: 1000 mL = 1 L, so 1050 mL = 1 L 50 mL

Write 50 in the mL column, carry 1 to the L column.

Step 2: Add litres: 1 + 3 + 4 = 8 L

Answer: 8 L 50 mL

Step-by-step method

1. Write the measurements in columns
2. Subtract the smallest units first
3. If the top number is smaller, borrow 1 from the next column (convert it first)
4. Continue subtracting until all columns are done

Example: Subtracting Length

Subtract: 12 km 200 m − 4 km 950 m

Step 1: Subtract metres: 200 m − 950 m is not possible, so borrow 1 km

1 km = 1000 m

Add: 1000 m + 200 m = 1200 m

Now subtract: 1200 m − 950 m = 250 m

Write 250 in the m column. Remember we now have 11 km.

Step 2: Subtract kilometres: 11 km − 4 km = 7 km

Answer: 7 km 250 m

Example: Subtracting Mass

Subtract: 6 t 200 kg − 2 t 300 kg

Step 1: Subtract kilograms: 200 kg − 300 kg is not possible, so borrow 1 t

1 t = 1000 kg

Add: 1000 kg + 200 kg = 1200 kg

Now subtract: 1200 kg − 300 kg = 900 kg

Write 900 in the kg column. Remember we now have 5 t.

Step 2: Subtract tonnes: 5 t − 2 t = 3 t

Answer: 3 t 900 kg

Example: Subtracting Volume

Subtract: 15 L 350 mL − 10 L 370 mL

Step 1: Subtract millilitres: 350 mL − 370 mL is not possible, so borrow 1 L

1 L = 1000 mL

Add: 1000 mL + 350 mL = 1350 mL

Now subtract: 1350 mL − 370 mL = 980 mL

Write 980 in the mL column. Remember we now have 14 L.

Step 2: Subtract litres: 14 L − 10 L = 4 L

Answer: 4 L 980 mL

• Always start adding or subtracting from the smallest unit (right side)
• When the sum of a column is 10 or more, convert and carry
• When the top number is smaller than the bottom number, borrow from the next column
• Make sure all measurements are in the same unit before adding or subtracting

In Tanzania, market vendors and shopkeepers use addition and subtraction of measurements every day. For example, a maize flour seller at the Mwanza market might have 15 kg 500 g of maize flour in a sack and a customer buys 8 kg 250 g. The seller must subtract to find that 7 kg 250 g of flour remains in the sack. This is how traders keep track of their goods accurately.