Chapter 7.5 (Mathematics 5)

Addition of decimals up to thousandths

Addition of decimals

Group Activity 3

In pairs, work out: 6.21 + 10.37

  1. Represent the decimal number 6.21 in an abacus.
  2. On the same abacus represent 10.37.
  3. Count the number of rings in hundredths, tenths, tens and ones.
  4. Discuss the results and share with other groups.

Example 6

Add:

a) 3.4 + 0.8

b) 0.354 + 4.293

Add thousandths: ​4 + 3 = 7.
​Write 7 in the thousandths column.
​Add hundredths: ​5 + 9 = 14.
Regroup 14 as 1 tenth and 4 hundredths.
​Write 4 in the hundredths column and 1 above 3.​
​Add tenths: 1 + 3 + 2 = 6.
​Write 6 in the tenths column.
​Add ones: 0 + 4 = 4.
​Write 4 in the ones column.

Exercise E

  1. 0.3 + 0.4 = 
  2. 0.6 + 0.2 = 
  3. 0.3 + 0.56 = 
  4. 0.79 + 0.2 = 
  1. 0.8 + 0.9 = 
  2. 0.6 + 0.7 = 
  3. 2.54 + 0.7 = 
  4. 1.23 + 0.9 = 

E3

Work out:
​

E4

Add:
​

E5

Work out:
​

  1. 4.625 + 2.74 = 
  2. 3.24 + 4.287 = 
  3. 12.33 + 5.147 = 
  4. 15.327 + 4.87 = 

1.5 kg  0.8 kg =  kg

2.6 l  1.75 l =  l

1.75 l  2.5 l =  l

Motorcycle