Year 5 measurement: six questions and the common mistakes

Six questions

1. How long is the pencil sharpener, in centimetres?

   Show the answer to question 1

   Answer: 3.2 cm

   Why:

   Each centimetre is split into 10 millimetres. The right end is at 4 cm and 2 small marks, which is 42 mm.

   The pencil sharpener starts at 1 cm, not at 0. 42 − 10 = 32 mm. 32 mm is 32 ÷ 10 = 3.2 cm.

   Common mistakes:

   • 320: It looks as if you multiplied instead of dividing. Dividing by 10, 100 or 1,000 makes a number smaller: the digits move to the right.
   • 32: Your digits are right, but in the wrong columns: your answer is 10 times too big.
   • 0.32: Your digits are right, but in the wrong columns: your answer is 10 times too small.

2. 9.06 km is 9 km and how many metres?

   Show the answer to question 2

   Answer: 60 m (also accept 9 km 60 m, 9 km and 60 m)

   Why:

   The 9 km is the whole part; 0.06 km is what is left. 1 km = 1,000 m, so 0.06 × 1,000 = 60 m.

   So 9.06 km is 9 km 60 m.

   Common mistakes:

   • 06: It looks as if you copied the digits after the decimal point into the smaller unit. Those digits are part of one whole of the bigger unit, so change that part: 0.25 of 1,000 is 250, not 25.

3. Zainab says: 0.373 kg is 37.3 g.

   Is Zainab right? Write the correct answer, not just yes or no.

   Show the answer to question 3

   Answer: 373 g · "No, 373 g" is right too; "No" on its own scores nothing

   Why:

   1 kg = 1000 g, so multiply: 0.373 × 1000 = 373 g.

   Zainab's answer was not right: the correct answer is 373 g.

   Common mistakes:

   • 0.000373: It looks as if you divided instead of multiplying. A smaller unit takes more of them to make the same amount, so the number gets bigger: the digits move to the left.
   • 3,730: Your digits are right, but in the wrong columns: your answer is 10 times too big.
   • 37.3: Your digits are right, but in the wrong columns: your answer is 10 times too small.

4. How long is the worm, in centimetres?

   Show the answer to question 4

   Answer: 2.1 cm

   Why:

   Each centimetre is split into 10 millimetres. The right end is at 5 cm and 1 small mark, which is 51 mm.

   The worm starts at 3 cm, not at 0. 51 − 30 = 21 mm. 21 mm is 21 ÷ 10 = 2.1 cm.

   Common mistakes:

   • 210: It looks as if you multiplied instead of dividing. Dividing by 10, 100 or 1,000 makes a number smaller: the digits move to the right.
   • 21: Your digits are right, but in the wrong columns: your answer is 10 times too big.
   • 0.21: Your digits are right, but in the wrong columns: your answer is 10 times too small.

5. Which is longer: 96 cm or 0.96 m?

   • A 96 cm
   • B They are the same length
   • C 0.96 m
   Show the answer to question 5

   Answer: B · They are the same length

   Why:

   Put both in the same unit. 0.96 m is 96 cm, the same as 96 cm.

   Common mistakes:

   • A · 96 cm: It looks as if you compared the numbers without their units. A bigger number can be a smaller amount when its unit is smaller: write both in the same unit first, then compare.

6. Convert 463 cm into m.

   Show the answer to question 6

   Answer: 4.63 m

   Why:

   100 cm = 1 m, so divide: 463 ÷ 100 = 4.63 m.

   Common mistakes:

   • 46,300: It looks as if you multiplied instead of dividing. Dividing by 10, 100 or 1,000 makes a number smaller: the digits move to the right.
   • 46.3: Your digits are right, but in the wrong columns: your answer is 10 times too big.
   • 0.463: Your digits are right, but in the wrong columns: your answer is 10 times too small.