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The number one-hundred-and-one
101 centimetres is the same as 1.01 metres.

Decimal Numbers 2 (Difficult)

Explore how decimals reveal the hidden maths of our solar system. Discover how tiny numbers explain vast distances and planetary orbits.

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Fascinating Fact:

Mercury’s year lasts only 88 Earth days, while Neptune’s lasts 60,190. Decimals show how time varies across the solar system.

In 11 Plus Maths, decimals help compare huge and tiny values. Astronomers use decimals to measure distances, orbital speeds, and time with incredible accuracy across planets.

  • Decimal: A number that includes a point to separate whole numbers from fractions, like 3.14.
  • Orbit: The curved path of a planet or object around a star or planet.
  • Ratio: A way to compare two quantities, often written using decimals to show precision.
How are decimals used in astronomy?

Scientists use decimals to measure planetary distances, time periods, and rotation speeds, allowing precise comparisons between planets like Earth and Mercury.

Why do planets have different year lengths?

Each planet’s year depends on how long it takes to orbit the Sun. The farther it is from the Sun, the longer its orbit and year.

What is a real-life example of decimals in space?

NASA uses decimals to record spacecraft positions, fuel use, and travel distances, ensuring accuracy in every space mission.

1 .
What is 21.63 kilometres in centimetres?
2,163 cm
21,630 cm
2,163,000 cm
216,300 cm
Convert km to m by multiplying by 1,000. So, 21.63 x 1,000 = 21,630
Next, convert m to cm by multiplying by 100. So, 21,630 x 100 = 2,163,000
2 .
How many kilograms are there in 2.3 tonnes?
2,300,000
23,000
230
2,300
There are 1,000 kg in 1 tonne, so in 2.3 tonnes there are 1,000 × 2.3 = 2,300 kg
3 .
What is 14,253 centimetres in metres?
1,425.3 m
1.4253 m
14.253 m
142.53 m
There are 100 cm in 1 m, so in 14,253 cm there are 14,253 ÷ 100 = 142.53 m
4 .
How many square centimetres are there in 15.3 square metres?
1,530 cm²
15,300 cm²
153,000 cm²
1,530,000 cm²
Be careful of squares! There are 100 cm in 1 m, so in 1 sq m there are 100 × 100 = 10,000 sq cm. In 15.3 sq m there are 15.3 × 10,000 = 153,000 sq cm
5 .
How many kilograms are there in 7,531.09 grams?
0.753109 kg
7.53109 kg
75.3109 kg
753.109 kg
There are 1,000 g in 1 kg, so in 7,531.09 g there are 7,531.09 ÷ 1,000 = 7.53109 kg
6 .
What was 987.654 divided by if the answer is 0.987654?
1,000
100
10,000
10
The rule for dividing by a whole number beginning with 1 and followed by one or more zeros, e.g. dividing by 10, 100, 1,000, ... is as follows: When dividing by such a number, move the digits to the right by the same number of zeros as in the number: 987.654 ÷ 1,000 = 0.987654: the digits have moved three places to the right = the number of zeros in one thousand
7 .
What was 9.87654 multiplied by if the answer is 987.654?
100
10
1,000
10,000
The rule for multiplying by a whole number beginning with 1 and followed by one or more zeros, e.g. multiplying by 10, 100, 1,000, ... is as follows: When multiplying by such a number, move the digits to the left by the same number of zeros as in the number: 100 × 9.87654 = 987.654: the digits have moved two places to the left = the number of zeros in one hundred
8 .
What does 0.00025 have to be multiplied by to give 2.5?
1,000
10,000
100,000
100
For 0.00025 to become 2.5, the digits will have to move 4 places to the left. You will have to multiply 0.00025 by 10,000 - which has 4 zeros
9 .
The marathon is a race over a distance of 42.195 kilometres. How many metres is that?
4,219,500 m
421,950 m
42,195 m
4,219.5 m
There are 1000 m in 1 km, so in 42.195 km there are 227.65 × 1,000 = 42,195 m
10 .
A gold bar weighs ‪12,442.61‬ grams. How many kilograms does a gold bar weigh?
1.244261 kg
1,244.261 kg
124.4261 kg
12.44261 kg
There are 1,000 g in 1 kg, so in 12,442.61 g there are 12,442.61 ÷ 1,000 = 12.44261 kg
Author:  Frank Evans (Specialist 11 Plus Teacher and Tutor)

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