# math calculation assistance please.

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Hello guys,

I am in my third semester currently. Today I had my math calculation test. I didn't think it was too bad but i missed it by 1 question. So I need some help. I need to pass the test, otherwise I will not be able to pass medications in clinical. We have a math calculation test each semester. Here is the question I struggled with:

1.Questions that ask at what time should the medication end.

example: 1.An IV of 50 mL of D5W with Ancef 1 GM is to infuse at 100mL/hr. The IVPB started at 0730.

What time will the infusion end?

-How do we calculate these? I saw a similar question on my test for the first time and I put my answer as 0900 but the answer was 0920. What? How? Help? unfortunately, i don't remember the exact work problem but there must be formula or something.Does anyone know a website where I can find problems specifically like this one or can someone give me one to practice.

Editorial Team / Admin

6 Articles; 11,338 Posts

Specializes in OR, Nursing Professional Development. Has 18 years experience.

What did you do to come up with your answer? If you show your work, we can help you figure out where you went wrong.

92 Posts

For this problem, it's 50 ml and it started at 0730. Since it is to be infuse at 100 ml. I was thinking it probably will take 2 hours 1 be infused because 50 is half of 100. It should end at 0830. maybe? Is there a formula to go by, is there a website I can go to find questions like these.

92 Posts

For this problem, it's 50 ml and it started at 0730. Since it is to be infuse at 100 ml. I was thinking it probably will take 1 hour be infused because 50 is half of 100. It should end at 0830. maybe? Is there a formula to go by, is there a website I can go to find questions like these.

563 Posts

Specializes in NICU, RNC.

50ml infusing at 100ml/hr would complete in 30 minutes, and would end at 0800. Not at all sure how your professors did the math to have it ending at 0920, so the only advice I can give you is to speak with your instructor. Either you're remembering the problem wrong, or they did some really wonky math to get that answer.

92 Posts

I was saying 0920 was for another similar problem we had. How did you get 0800 can you explain please?

563 Posts

Specializes in NICU, RNC.

I will attempt to show the work here, I generally do these in my head, so it took a sec to remember how to appropriately write it out. :)

1 hr x 60 mins x 50 mL = 30 mins

100 mL 1 hr

Infusion would end at 0800 if begun at 0730

To show how this works with not so even numbers, lets say it's running at 125 ml/hr

1 hr x 60 mins x 50 mL = 24 mins

125 mL 1 hr

Infusion would end at 0754 if begun at 0730

I hope this helps, the formatting is hard to do on the computer.

563 Posts

Specializes in NICU, RNC.
I was saying 0920 was for another similar problem we had. How did you get 0800 can you explain please?

Ok, that makes more sense.

Editorial Team / Admin

6 Articles; 11,338 Posts

Specializes in OR, Nursing Professional Development. Has 18 years experience.

It's a lot like an algebra equation where you are solving for X. In this question, X is the amount of time the infusion will run. See if you can set up an equation where you would solve for X with the information you have. There is no equation that is going to give you a time of day- that requires a second step of adding X to the time the medication was starting.

Editorial Team / Admin

6 Articles; 11,338 Posts

Specializes in OR, Nursing Professional Development. Has 18 years experience.
I will attempt to show the work here, I generally do these in my head, so it took a sec to remember how to appropriately write it out. :)

1 hr x 60 mins x 50 mL = 30 mins Infusion would end at 0800 if begun at 0730

100 mL 1 hr

To show how this works with not so even numbers, lets say it's running at 125 ml/hr

1 hr x 60 mins x 50 mL = 24 mins Infusion would end at 0754 if begun at 0730

125 mL 1 hr

I hope this helps!

Unfortunately your spacing is off for the use of underlining. It's better to use the / instead.

Editorial Team / Admin

6 Articles; 11,338 Posts

Specializes in OR, Nursing Professional Development. Has 18 years experience.

Some equations that may help

• flow rate (mL/hr) = total volume (mL) Ã· infusion time (hr)
• infusion time (hr) = total volume (mL) Ã· flow rate (mL/hr)
• total volume (mL) = flow rate (mL/hr) Ã— infusion time (hr)

Can you tell which one of these you would use to solve your problem?

91 Posts

Has 1 years experience.

.An IV of 50 mL of D5W with Ancef 1 GM is to infuse at 100 mL/hr. The IVPB started at 0730.

What time will the infusion end?

Formula

Total infusion time= Total number of mL to infuse divided by mL/hr infusion rate

= 50 mL/100 mL/hr = 0.5 hr

0.5 hr x 60 min/hr = 30 mins

Infusion started at 0730 add 30 minutes, it will end at 0800

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