Addition

CBC Grade 5 Mathematics — Addition

Lesson Objectives

By the end of this topic, a learner should be able to:

• Add up to three 6-digit numbers without regrouping
• Add up to two 6-digit numbers with regrouping
• Estimate sums by rounding addends before adding
• Create number patterns involving addition
• Appreciate the use of addition in everyday life

Addition

Adding puts numbers together to find a total. In Grade 5 we add numbers with up to six digits.

a) Setting it out

Write the numbers one under the other.

Line up the columns from the right. Ones under ones, tens under tens, and so on.

If one number is shorter, leave the space empty or write a zero. Do not push it left.

Draw a line and add each column, starting from the right.

b) Adding without regrouping

Sometimes each column adds to 9 or less. Then simply write the answer under the line.

Add three numbers the same way, one column at a time.

c) Adding with regrouping

A column may add to 10 or more. Then only the last digit goes under the line. The rest is carried into the next column.

Write the carried digit small, above the next column, so you remember it.

Forgetting to add the carry is the commonest mistake. Always look for it before moving on.

d) Estimating the sum

An estimate is a quick rough answer. It tells you whether your careful answer is sensible.

Round each number first, then add.

The estimate is 7 900 and the real answer is 7 931. They are close, so the answer looks right.

Suppose your answer were 793 or 79 310. The estimate would show at once that something was wrong.

Estimate first, then calculate. Then you know what to expect.

e) Number patterns

A pattern follows a rule.

In 5, 9, 13, 17 the rule is "add 4".

To find the rule, look at the gap between one number and the next.

Then use the rule to carry the pattern on. The next two are 21 and 25.

f) Where this is used

Adding up a shopping bill. Counting money collected. Working out a total score. Finding how many people attended over several days.

:::checkpoint Check yourself

1. Work out 34 271 + 15 468.
2. Estimate 5 218 + 2 894 by rounding to the nearest hundred.
3. What does it mean to carry a digit?
4. Give the next two numbers in 7, 12, 17, 22. :::

Definitions

• Regrouping (carrying) — moving a value of 10 from one column into the next, when a column's total is 10 or more.
• Addend — a number being added to another.
• Estimate — an approximate answer, found by rounding before calculating.

Must Remember

1. Always add from the ones column first — carrying only works in that direction.
2. A carried 1 must be added into the next column's total.
3. Round every addend the same way before estimating.
4. If an estimate and exact answer are far apart, re-check the exact working.

Conclusion

Work column by column from the right, carry a 10 whenever a column overflows past 9, and use estimation as a running check on the answer.