179 + 642 =
6 130 + 150 + 190 + 250 + 80 + 225 =
7 125 + 145 + 155 + 68 + 95 + 300 =
8 500 + 200 + 150 + 45 + 60 + 120 + 397 =
9 220 + 140 + 50 + 65 + 72 + 168 =
10 85 + 33 + 120 + 235 + 128 + 50 =
11 During the course of a morning, a patient drinks the following amounts of fluid: tea 180 millilitres, orange 100 millilitres, water 120 millilitres, milk 125 millilitres and coffee 150 millilitres. What is the total amount of fluid that the patient receives?
12 A patient has a chest drain following surgery. Over the course of 24 hours, it drains: 125 millilitres, 70 millilitres and 40 millilitres. In addition, the patient is nauseous and vomits on four occasions, losing the following amounts of fluid: 250 millilitres, 150 millilitres, 120 millilitres and 90 millilitres. What is the total amount of fluid lost over the 24-hour period?
2.4 Subtraction
Subtractions involve taking one number away from another. In the clinical environment they are used in the calculation of fluid balance records to determine if the patient is in a negative or positive state of fluid balance and they are also used to calculate the stock levels of controlled drugs following administration.
The same basic rules apply as they did for additions. It is important that the digit positions are maintained to avoid errors and this is where the use of columns can help. Usually, but this is not always the case, a smaller number is taken away from a larger number, so place the larger number at the top and the smaller number below it. When calculating fluid balance records, for example, the fluid loss from the body can be greater than the input and so in this case you are calculating the difference between the input (this number at the top) and the output (this number at the bottom). Chapter 5 covers this in more detail.
SENSE CHECK
Don’t forget to check that you haven’t made a basic error with your calculation. If you subtract, the answer must be less than the number that you started with.
Use the following procedure to check your subtraction answers:
add your answer to the number that you took away
for example 34 – 22 = 12 so therefore 12 + 22 = 34.
| EXAMPLE 2.4 |
Method
The subtraction 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 3 hundreds, 7 tens and 4 ones, or 374.
Checking
To check your answer: 374 + 311 = 685.
Not all subtractions are straightforward because there will be times when the calculation requires you to take a larger number from a smaller number; see Example 2.5 in which you need to take 5 from 3.
| EXAMPLE 2.5 |
Method
As before, the subtraction is calculated vertically from right to left, starting under the ‘ones’ column.
Process
Starting with the ‘ones’ column:
5 – 3 =
You cannot take 5 from 3 because 3 is less than 5. The way around this is to borrow 1 ‘ten’ from the 8 ‘tens’ under the ‘ten’ column. When this is transferred to the ‘ones’ column, this is added to the 3 to give 13. The usual way of doing this is to write a small ‘1’ by the 3 under the ‘ones’ column. The 8 under the ‘tens’ column needs to be reduced to 7 to account for 1 ten being borrowed by the ‘ones’ column. This involves crossing out the 8 and replacing it with a 7.
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
