Decimals

Syllabus tag: Kenya CBC | Grade 6 Mathematics | Strand 1.0 Numbers | Sub-Strand 1.5 Decimals (12 Lessons)

Lesson objectives

By the end of this topic, you will be able to:

• Identify decimals up to ten-thousandths
• Round off decimals to 3 decimal places
• Convert between decimals and fractions, and between decimals and percentages
• Add and subtract decimals up to 4 decimal places
• Appreciate the use of decimals in real life

Decimals

A decimal shows parts of a whole using a point. The digits after the point get smaller each step.

a) The places

The first place after the point is tenths.

The second is hundredths, the third thousandths, and the fourth ten-thousandths.

Each place is ten times smaller than the one before it.

b) Reading a decimal

Read the whole part, then say "point", then read each digit on its own.

So 3.472 is read as three point four seven two. Do not say "three point four hundred and seventy-two".

c) Rounding to 3 decimal places

Look at the digit after the place you want.

If it is 5 or more, round up. If it is less than 5, leave the digit alone.

Then drop everything after.

d) Decimals and fractions

A decimal is just a fraction with a bottom of 10, 100 or 1 000.

So 0.75 is 75 hundredths, which is 75/100, which simplifies to 3/4.

To turn a fraction into a decimal, divide the top by the bottom. For 2/5, divide 2 by 5 to get 0.4.

e) Decimals and percentages

Per cent means out of 100.

To change a decimal into a percentage, multiply by 100. So 0.75 becomes 75%.

To change a percentage into a decimal, divide by 100. So 30% becomes 0.3.

Some worth knowing: 0.5 is 50%, 0.25 is 25%, and 0.1 is 10%.

f) Adding and subtracting

Line up the decimal points, one under the other.

Fill any gaps with zeros so both numbers have the same number of places.

To add 3.2 and 1.456, write 3.200 and 1.456. Then add to get 4.656.

Keep the point in the answer directly below the points above it.

g) Where this is used

Money uses two decimal places. Measurements of length and mass are decimal. Test scores are often given as percentages.

Words to know

• Decimal point — the dot separating the whole-number part of a number from its fractional part.
• Tenths, hundredths, thousandths, ten-thousandths — the place value columns immediately to the right of the decimal point.
• Rounding — expressing a decimal to fewer decimal places by checking the next digit along.

:::checkpoint Check yourself

1. How many decimal places does 5.0842 have?
2. Round 6.3517 to 3 decimal places.
3. Write 0.6 as a fraction in its simplest form.
4. Write 0.35 as a percentage. :::

Bridge to practice

Try the exercises below — reading place value, rounding, converting, and adding/subtracting decimals, the same five skills covered above.