This gives the answer of 3 hundreds, 3 tens and 8 ones, or 338.
Checking
To check your answer: 338 + 445 = 783.
| EXAMPLE 2.6 |
When monitoring a patient’s state of hydration, fluid balance charts are invaluable. These involve calculating the amount of various types of fluid input and output as well as the total input and output from the body.
The overall fluid balance is calculated by subtracting the output from the input. If a patient’s total input over 24 hours was 2455 millilitres and their output was 2260 millilitres, you can calculate their fluid balance as follows.
Method
As before, the subtraction is calculated vertically from right to left, starting under the ‘ones’ column. Note that an additional column for ‘thousands’ has been included because the numbers are in the thousands.
Process
Moving left to the ‘tens’ column:
5 – 6 =
You cannot take 6 from 5, because it is a lower number. The way around this is to borrow 1 ‘hundred’ from the 4 ‘hundreds’ under the ‘hundreds’ column. When this is transferred to the ‘tens’ column, this is added to the 5 to give 15. This is recorded by writing a small ‘1’ by the 5 under the ‘tens’ column. The 4 under the ‘hundreds’ column needs to be reduced to 3 to account for 1 hundred being borrowed by the ‘tens’ column. This involves crossing out the 4 and replacing it with a 3.
This gives the answer of 0 thousands, 1 hundred, 9 tens and 5 ones, or 195. Therefore the patient’s input was 195 millilitres more than their output.
Checking
To check your answer: 195 + 2260 = 2455.
Self-assessment test 2.3: subtraction
The recap questions below will help to consolidate your learning about subtractions. Answers can be found at the end of the book.
1 155 – 42 =
2 1276 – 165 =
3 916 – 817 =
4 96 – 58 =
5 117 – 99 =
6 2139 – 126 =
7 6483 – 5261 =
8 2912 – 1915 =
9 792 – 689 =
10 542 – 454 =
11 If a patient’s total fluid input over 24 hours was 3205 millilitres and their output was 2410 millilitres, what is their overall fluid balance?
12 A patient takes morphine sulphate solution 10 mg in 5 millilitres orally, six times each day. The ward stock bottle contains 250 millilitres. How much will be left in the bottle after seven days?
2.5 Multiplication
Multiplication is the same as repeatedly adding the same number together, for example, 5 × 12 is the same as 12 + 12 + 12 + 12 + 12, but the process is less time consuming. Multiplications are used to calculate fluid balance charts where the same volume has been given repeatedly and when calculating drug doses that are prescribed per kilogram of body weight.
Many people remember their ‘times tables’ from school. If you didn’t learn these or have forgotten them, you might find that a copy of the ‘multiplication grid’ in Appendix 5 acts as a valuable resource. If you don’t know your times tables, it’s worth practising them until you are confident that you can do simple multiplications in your head.
When multiplying two or more numbers together, the calculation can be performed in any order, so 25 × 4 gives the same answer as 4 × 25.
To check your multiplications
Divide your answer by one of the numbers you multiplied.
For example 6 × 4 = 24 therefore 24 ÷ 4 = 6.
| EXAMPLE 2.7 |
Method
The multiplication is calculated vertically from right to left, starting under the ‘ones’ column and involves three individual calculations, one for the ‘ones’ column, one for the ‘tens’ column and a final calculation for the ‘hundreds’ column.
Process
This gives the answer of 4 hundreds, 6 tens and 8 ones, or 468.
Checking
To check your answer: 468 ÷ 2 = 234.
Not all multiplications are as straightforward as this. There will be times when the calculation results in ten or more in a column, such as in Example 2.8.
| EXAMPLE 2.8 |
Method
As before, the multiplication is calculated vertically from right to left, starting under the ‘ones’ column and involves three individual calculations, one for the ‘ones’ column, one for the ‘tens’ column and a final calculation for the ‘hundreds’ column.
Process
The number ‘15’ is made up of one ‘ten’ and five ‘ones’. Because this column is only used to record the ‘ones’, the five ‘ones’ are recorded here and the ‘ten’ carried over to the ‘tens’ column. The usual way of doing this is to write a small ‘1’ below the 2 under the ‘tens’ column.
This gives the answer of 3 hundreds, 7 tens and 5 ones, or 375.
Checking
To check your answer: 375 ÷ 3 = 125.
This process works well when the multiplication involves one number that is less than ten. When both of the numbers to be multiplied together are greater than ten, an extra stage of calculation is necessary.
| EXAMPLE 2.9 |
A fluid balance chart shows that a patient’s oral intake in one 24-hour period was 11 glasses of water. Each glass measures 85 ml. What is the total oral intake?
This calculation involves multiplying 85 and 11.
Method
As before, the multiplication is calculated vertically from right to left, making sure that individual digits are kept in position within the columns. The terms ‘ones’, ‘tens’ or ‘hundreds’ column used within the explanation only refer to the top number