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Math help from the Learning Centre

This guide provides useful resources for a wide variety of math topics. It is targeted at students enrolled in a math course or any other Centennial course that requires math knowledge and skills.

General Dosage Rounding Rules

Weight, Fluid Oral Volume and Temperature

  • When converting body weight from lb to kg, round it to the nearest tenth.
  • For fluid oral volume and temperature, round it to the nearest tenth as well.

Note: tenth stands for the first place after the decimal point. Refer to Decimals for detailed information.

Example: 

30 lb = 13.6078 kg

To round 13.6078 to the nearest tenth, we look at the number on hundredth. If this number is in the range of 5 to 9, we round it up  by adding 1 to the tenth. Otherwise, we round it down to keep the tenth unchanged.

Since 0 is on hundredth, we round it down to 13.6:

30 lb = 13.6 kg

Tablets/Capsules

  • Round unscored tablets to the nearest whole number.
  • Scored tablets maybe broken in half, so numbers of scored tablets should be rounded to the nearest half tablet.

Example 1: Unscored

Order: 600 mcg

In hand: 250 mcg/tablet

Dosage: 2.4 tablets

To round 2.4 to a whole number, we check the number on tenth. Since it is 4 on tenth, round down to 2 tablets.

 

Example 2: Scored

Order: 600 mcg

In hand: 250 mcg/tablet

Dosage: 2.4 tablets

Since 2.4 is between 2.25 and 2.50, 2.5 is the nearest half. Round it up to 2.5 tablets.

Fluid Injectable Volume

  • Round to the nearest hundredth if the volume is less than 1 mL;
  • Round to the nearest tenth if the volume is greater than 1 ml.

Example 1:

0.345 mL

0.345 is less than 1, so it should be rounded to the nearest hundredth. On thousandth it is a 5, so round it up to 0.35 mL.

 

Example 2:

1.345 mL

1.345 is greater than 1, so it should be rounded to the nearest tenth. On hundredth it is a 4, so round it down to 1.3 mL.

Intravenous

  • Round to the nearest whole number for piggyback infusion, such as flow rate in gtt/min or mL/hr, and drop factor in gtt/mL as drops cannot be fractionated.
  • Round to the nearest tenth for dose -based flow rate such as mg/mL.

Examples:

15.25 gtt/min should be rounded to 15 gtt/min;

249.71 mL/hr should be rounded to 250 mL/hr;*

20.612 gtt/mL should be rounded to 21 gtt/mL;

0.625 mg/mL should be rounded to 0.6 mg/mL.

 

Note: In the second example, we need to round 249.71 to a whole number. It is 9 on the place of ones, so when rounding it up we get 10, which means we will write 0 on the place of ones and add one to the place of tens. Therefore we finally got 250.

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