For questions 1 to 5 you will be given a sum AND an answer. Use your ability to estimate to work out which ones are probably right.
- 32.5 × 17.68 = 574.6 This is probably right. It is the exact answer if you check.
- 153.67 ÷ 37.6 = 0.409 This is obviously wrong... 160 ÷ 4 = 4 so the answer should be around 4, not 0.4.
- 3.25 ×104 × 1.2 ×10-8 =3.9 ×10-4 This is probably right. It is the exact answer if you check.
- 3.25 ×104 ÷ 1.2 ×10-8 = 2.71 trillion This is about right. In fact, to 3 sig figs it is the right answer.
- 153.67 × 37.6 = 6777.992 This could be right. 150 × 40 = 6000. The exact answer is 5777.992: it is worth remembering that estimating will not catch every mistake!
Many drugs are given in standard doses, e.g. "take two paracetamol every four hours" because they have a fairly wide range of doses at which they are effective but not dangerous. Some other drugs, many of those given to newborn babies, and certain drugs given to treat cancer or similar are given with much more critical doses. These are usually given by injection. Doses are calculated according to the formula What You Want ÷ What You've Got × What It's In. In addition, the amount you need to give might be calculated from Body Mass × Amount Per kg.
Whilst you won't be expected to remember these formulae (unless you are a nurse, medic, vet or similar), use them to calculate amounts of drugs to give in questions 6-10. You should be able to do almost all of this without a calculator. If you are following the course, please feel free to use a calculator but ONLY for the division part as we have not covered that yet.
NOTE: The drugs are deliberately called drug A, drug B etc. and although the numbers are reasonable they have not been selected to represent any particular drug.
- Drug A is given at 5µg/kg body weight. The patient weighs 60 kg. You have 500 µg in 10ml. You must give 5 × 60 = 300µg. 300÷500×10 = 6ml.
- The patient must be given 850 ng of Drug B. Stock supply is 1µg in 2ml. 850÷1000×2=1.7ml. Remember there are 1,000ng in 1µg. If you try 850÷1×2 = 170ml you might think that giving 85 vials of the drug might be wrong...
- Drug C is given at 7.5mg/kg and the patient weighs 78kg. You have 1.0g in 1ml. You need 7.5×78=497.25mg. 497÷1000×1=0.49725ml or (more likely) 497µl. The 1000mg in 1g rule applies here.
- Drug D is given at 0.15 µg/kg. The patient weighs 7.2 kg. You have 25µg in 0.5ml. You need 0.15×7.2=1.08µg. 1.08÷25×0.5=21.6µl. (This is an unlikely dose, it is very small, but paediatric treatments can be.)
- Drug E is given at 0.15 ng/kg. The patient weighs 72 kg. You have 250 ng in 5ml. You need 0.15×72=10.8ng. 10.8÷250×5=0.216ml or 216µl. (This too is an unlikely dose, it suggests there are something like 20 doses in one supply, it is more normal to have about one dose in one supply, but you can find situations like this still.)
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