Distance Learning 21

IWCF UK Branch Distance Learning Programme DRILLING CALCULATIONS

Part 1 Section 3 32 of 211

3.3 Subtraction This is concerned with taking things away.

The symbol we use is -, for example 3 1 = 2.

Example

The five drinks that you bought before costs you 10.77. You give the barman 15 then you take away the 10.77 to calculate how much change you should have.

.

(4.23 is the difference between 15 and 10.77)

15 10.77- = 4.23

Example

The eleven sacks of mud chemicals added to the drilling mud previously were removed from a pallet holding 30 sacks.

How many sacks are left?

30 - 11 = 19



Example Calculator subtraction 1

3 6 5 - 1 4 =

The display will show

351.

Example Manual Subtraction 1

Subtract 14 from 365 (365- 14)

The calculation should be written in the same way as the addition calculation with the units figures lined up underneath each other at the right hand side.

Start with the units column, 4 from 5 is 1. This is placed under the top line in the units column.

Next take the tens column, 1 from 6 is 5. This is placed under the top line in the tens column.

Next take the hundreds column, 0 from 3 is 3. This is placed under the top line in the hundreds column.

The answer is 351.

One way to check you are correct is to add the answer and the number taken away together this should equal the original number.

e.g. 351 + 14 = 365

HTU365 14 1

HTU365 14 51

HTU36514

351



Example - Manual subtraction 2

Subtract 86 from 945 (945 86

The calculation should be written in the same way as the addition calculation with the units figures lined up underneath each other at the right hand side.

Start with the units column, 6 is larger than 5 and wont go so we have to borrow one from the tens column. This is added to the 5 to get 15. We can then take 6 away from 15 to get 9. This is written under the line at the bottom of the units column.

The ten that we borrowed now has to be paid back. This can beshown in two ways

The ten is paid back at the bottom. The 1 is added to the 8 to make 9, this wont go into 4 so we borrow again this time from the hundreds column. This is added to the 4 to become 14, 9 from 14 is 5. The 5 is put at the bottom of the tens column and the borrowed 10 is paid back at the bottom of the hundreds column.

In the second method we cross off the figures on the top row.

You should use whichever you are most familiar with.

The second method can be confusing when dealing with zeros i.e. take 4 away from 600 (600 4), 4 from 0 wont go so we have to borrow from the next column. As the next column is also a 0 you have to go across the columns until you reach the 6. The 6 is crossed out and 5 is put in, 1 is put next to the 0 in the next column. This is then crossed out and replaced by 9 as we borrow a ten. We then continue as before.

HTU945 86 859

HTU945 86 9

H T U 9 4 5 8 6 1

8 5 9

98435 8 68 5 9

600 4 596

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Distance Learning 21