Addition/subtraction

Worked solution

1. 1

   Match the decimal places.

   $12.8=12.80$

   A zero hundredths digit makes the place-value alignment explicit.

2. 2

   Add hundredths and tenths.

   $7+0=7,6+8=14$

   Fourteen tenths regroup as one whole and four tenths; seven hundredths remain.

3. 3

   Include the regrouped whole.

   $5+12+1=18$

   The extra whole from the tenths column must be added to the whole-number parts.

4. 4

   Write the complete sum.

   $5.67+12.80=18.47$

   The result has eighteen wholes, four tenths and seven hundredths.

Worked solution

1. 1

   Split the amount to subtract.

   $7.86=7.80+0.06$

   Separating six hundredths gives two manageable subtractions.

2. 2

   Subtract the first part.

   $20.05-7.80=12.25$

   Removing eight whole units would leave 12.05; adding back 0.20 gives 12.25.

3. 3

   Subtract the remaining hundredths.

   $12.25-0.06=12.19$

   Six hundredths are still to be removed from the original 7.86.

4. 4

   Check by adding back.

   $12.19+7.86=20.05$

   The inverse operation restores the starting number, confirming 12.19.