Decimals and rounding: weighing rice at the shop
Put 1 kg bags, 100 g packets and 10 g scoops of rice on a scale to build decimals, then round the weight for the bill.
Core concept
In short: Weigh rice to learn decimal places and how to round numbers.
In a decimal, each place is ten times smaller than the one to its left; rounding looks at the next place to decide
Topic: Decimals
A shopkeeper weighs rice with 1 kg bags, 100 g packets and 10 g scoops. A 100 g packet is one tenth of a kilogram (0.1 kg) and a 10 g scoop is one hundredth (0.01 kg). So 2 bags, 4 packets and 7 scoops weigh 2.47 kg: 2 ones, 4 tenths and 7 hundredths, which is also 247/100 kg or 2470 g. To round to the nearest kg, look at the tenths: 5 or more rounds up, less than 5 rounds down. To round to the nearest 0.1 kg, look at the hundredths.
What you will learn
- Read and write decimals using place value: ones, tenths and hundredths.
- Change a decimal to a fraction with denominator 100 and to grams.
- Round a decimal to the nearest whole number and to one decimal place.
Before you start
- Place value of whole numbers; 1 kg = 1000 g.
Materials
- Rice and small bags or packets
Equipment
- A kitchen scale
Procedure
- Tap − or + under the bags, packets and scoops to change what is on the scale.
- Read the scale, the place-value table and the weight in grams.
- Tap the chip to round to the nearest kg or to the nearest 0.1 kg, and watch the number line.
- Record 2.47 kg, then 2.47 kg rounded to 0.1 kg, a weight that rounds up to 3 kg, and 0.75 kg.
How this simulation is simplified
- A bag is exactly 1 kg, a packet 100 g and a scoop 10 g.