[NanaMG]

I have a chemistry problem:   A dose of a drug for children is 3.5 mg. per kologram (3.5 mg/kg) of body weight every 6 hours.  If the child weighs 12 kg., how many milligrams would be given in a 24 hour period.  

This looked pretty simple to me and I calculated 3.5 mg x 4 times a day x 12 kg. and got 168 mg.  But the answer in the book was 1.7E2 mg. How in the world did they get that?  

Another problem was this one:
The tranquilizer Valium is sold in 2.0 mL syringes that contain 50.0 mg of drug per 1.0 mL of liquid (50.0 mg/1.0 mL). If a physician prescribes 25 mg of this drug, how many milliliters should be administered?

In my head I figured it was 0.50 mL, and that was the answer in the book.  I just don't know how to put the math together to get there.    

Can you help me?

[Borek]

This looked pretty simple to me and I calculated 3.5 mg x 4 times a day x 12 kg. and got 168 mg.  But the answer in the book was 1.7E2 mg. How in the world did they get that?

CHeck if that's not the same result, differing just by significant digits - 3.5 mg limiting number of digits in the final answer.

In my head I figured it was 0.50 mL, and that was the answer in the book.  I just don't know how to put the math together to get there.    

Can you help me?

No idea how to extract something from your head Try to analyze how you did it, as often intuition gives best approach.

[xiankai]

1st qn : your answer is correct. 1.7 E2 is calculator notation for 1.7 x 10^2
note the difference between E and e.
its probably given that way because 2 sig dig are required.

[themark]

Hello,

2nd question, This is probably what you did in your head

m1/v1 =m2/v2; m= mass drug, v= volume solution

hope this helps

[Blueshawk]

I have a chemistry problem:   A dose of a drug for children is 3.5 mg. per kologram (3.5 mg/kg) of body weight every 6 hours.  If the child weighs 12 kg., how many milligrams would be given in a 24 hour period.  

This looked pretty simple to me and I calculated 3.5 mg x 4 times a day x 12 kg. and got 168 mg.  But the answer in the book was 1.7E2 mg. How in the world did they get that?  

Another problem was this one:
The tranquilizer Valium is sold in 2.0 mL syringes that contain 50.0 mg of drug per 1.0 mL of liquid (50.0 mg/1.0 mL). If a physician prescribes 25 mg of this drug, how many milliliters should be administered?

In my head I figured it was 0.50 mL, and that was the answer in the book.  I just don't know how to put the math together to get there.    

Can you help me?

For the first question....

You got 168 mg  and the book had 1.7E2 mg.    1.7E2 mg = 170 mg.    
 
    Therefore the book must have rounded somewhere.

For question 2..


50mg/1ml = 25mg/Xml.       X is the unknown volume you need.   Cross multiply and you get...

50mg*X = 25mg*1ml       Divide by 50mg to solve for X....    X = (25mg*1ml)/50mg

X = 0.50...   Taadaa!!   so you would need 0.50 ml