Practice problems · Infusion time · 5 worked
Infusion time practice problems
An infusion time problem asks how long a volume takes at a given rate: the volume in milliliters divided by the rate in milliliters per hour. The result is often not a whole number of hours, so the rounding rule often decides the answer you write down.
The rounding rule on this page
Every answer here is rounded once, at the end, under one stated rule: nearest tenth, half rounds up, except tablets and capsules, rates in milliliters per hour and drip rates in drops per minute, which go to the nearest whole number, half rounds up. Your program's rule may differ, and on an exam it is the one that counts.
Work each problem on paper first, then open its solution. Each one is one of the 20 problems in DoseReady's Infusion time family, with the numbers the app drew for it.
No licensed clinician has reviewed the problem set. Where a problem and its source disagree, trust the source and what your program teaches.
Problem 1 of 5
A bag of normal saline holding 1,000 mL is infusing at 75 mL per hour. How many hours will the infusion take?
Show the worked solution
Dimensional analysis
1,000 × 1 ÷ 75 = 40/3
Ratio and proportion
75 mL is to 1 hr as 1,000 mL is to x
1,000 × 1 ÷ 75 = 40/3
x = 40/3 hr
Formula method
- D (desired)
- 1,000 mL
- H (have)
- 75 mL
- Q (quantity)
- 1 hr
D ÷ H × Q
1,000 × 1 ÷ 75 = 40/3
- The working comes to
- 40/3 hr (13.333… hr)
- The answer under the stated rule
- 13.3 hr
- Nearest tenth, half rounds up.
- Under “nearest hundredth, half rounds up” instead
- 13.33 hr
- Under “nearest whole number, half rounds up” instead
- 13 hr
What each slip gives here
- Decimal point one place out133.3 hr or 1.3 hr
- Conversion factor inverted75,000 hr
- Conversion skipped1,000 hr
- Rounded to the wrong precision13 hr or 13.5 hr or 13.25 hr or 13.33 hr or 13.333 hr
“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.
What this problem is built from
Problem 2 of 5
A unit of packed red blood cells holding 350 mL is transfusing at 100 mL per hour. How many hours will the transfusion take?
Show the worked solution
Dimensional analysis
350 × 1 ÷ 100 = 3.5
Ratio and proportion
100 mL is to 1 hr as 350 mL is to x
350 × 1 ÷ 100 = 3.5
x = 3.5 hr
Formula method
- D (desired)
- 350 mL
- H (have)
- 100 mL
- Q (quantity)
- 1 hr
D ÷ H × Q
350 × 1 ÷ 100 = 3.5
- The working comes to
- 3.5 hr
- The answer under the stated rule
- 3.5 hr
- Nearest tenth, half rounds up.
- Under “nearest whole number, half rounds up” instead
- 4 hr
What each slip gives here
- Decimal point one place out35 hr or 0.4 hr
- Conversion factor inverted35,000 hr
- Conversion skipped350 hr
- Rounded to the wrong precision4 hr
“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.
Problem 3 of 5
A rider of magnesium sulfate holding 4 g in 100 mL is infusing at 50 mL per hour. How many hours will the infusion take?
Show the worked solution
Dimensional analysis
100 × 1 ÷ 50 = 2
Ratio and proportion
50 mL is to 1 hr as 100 mL is to x
100 × 1 ÷ 50 = 2
x = 2 hr
Formula method
- D (desired)
- 100 mL
- H (have)
- 50 mL
- Q (quantity)
- 1 hr
D ÷ H × Q
100 × 1 ÷ 50 = 2
- The working comes to
- 2 hr
- The answer under the stated rule
- 2 hr
- Nearest tenth, half rounds up.
What each slip gives here
- Decimal point one place out20 hr or 0.2 hr
- Conversion factor inverted5,000 hr
- Conversion skipped100 hr
Problem 4 of 5
A bottle of five percent albumin holding 250 mL is infusing at 80 mL per hour. How many hours will the infusion take?
Show the worked solution
Dimensional analysis
250 × 1 ÷ 80 = 3.125
Ratio and proportion
80 mL is to 1 hr as 250 mL is to x
250 × 1 ÷ 80 = 3.125
x = 3.125 hr
Formula method
- D (desired)
- 250 mL
- H (have)
- 80 mL
- Q (quantity)
- 1 hr
D ÷ H × Q
250 × 1 ÷ 80 = 3.125
- The working comes to
- 3.125 hr
- The answer under the stated rule
- 3.1 hr
- Nearest tenth, half rounds up.
- Under “nearest hundredth, half rounds up” instead
- 3.13 hr
- Under “nearest whole number, half rounds up” instead
- 3 hr
What each slip gives here
- Decimal point one place out31.3 hr or 0.3 hr
- Conversion factor inverted20,000 hr
- Conversion skipped250 hr
- Rounded to the wrong precision3 hr or 3.25 hr or 3.13 hr or 3.125 hr
“Rounded to the wrong precision” is the same working rounded to some other step, such as a half, a quarter or a hundredth, or left unrounded.
Problem 5 of 5
A postpartum oxytocin infusion bag holds 20 units in 1,000 mL. The pump is running at 125 mL per hour. How many hours will the bag last?
Show the worked solution
Dimensional analysis
1,000 × 1 ÷ 125 = 8
Ratio and proportion
125 mL is to 1 hr as 1,000 mL is to x
1,000 × 1 ÷ 125 = 8
x = 8 hr
Formula method
- D (desired)
- 1,000 mL
- H (have)
- 125 mL
- Q (quantity)
- 1 hr
D ÷ H × Q
1,000 × 1 ÷ 125 = 8
- The working comes to
- 8 hr
- The answer under the stated rule
- 8 hr
- Nearest tenth, half rounds up.
What each slip gives here
- Decimal point one place out80 hr or 0.8 hr
- Conversion factor inverted125,000 hr
- Conversion skipped1,000 hr
What this problem is built from
Practice under your own program's rules
In DoseReady you enter your program's passing score, notation and rounding rule once. Every answer is graded under that rounding rule, and each worked solution is written in your notation where the problem allows it.
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Other problem families
- Unit conversion practice problems for nursing students
- Tablet and capsule dosage calculation practice problems
- Oral liquid dosage calculation practice problems
- Injectable dosage calculation practice problems
- Reconstitution dosage calculation practice problems
- mL per hr IV rate practice problems
- IV drip rate practice problems (gtt/min)
- Weight-based dosing practice problems (mg/kg)