Question

exercise 1
(a) the recommended daily allowance (rda) of the trace metal magnesium is 410 mg/day for males. express this quantity in μg/day.
(b) for adults, the rda of the amino acid lysine is 12 mg per kg of body weight. how many grams per day should a 75 kg adult receive?
(c) a typical multivitamin tablet can contain 2.0 mg of vitamin b₂ (riboflavin), and the rda is 0.0030 g/day. how many such tablets should a person take each day to get the proper amount of this vitamin, if he gets none from other sources?
(d) the rda for the trace element selenium is 0.000070 g/day. express this dose in mg/day.

Explanation:

Step1: Convert mg to μg for magnesium

We know that 1 mg = 1000 μg. So, to convert 410 mg to μg, we multiply by 1000.
$410\times1000 = 410000$ μg

Step2: Calculate lysine amount for 75 - kg adult

The RDA of lysine is 12 mg/kg. For a 75 - kg adult, we multiply the RDA per kg by the body - weight. So, $12\times75=900$ mg. Then convert mg to g. Since 1 g = 1000 mg, $900\div1000 = 0.9$ g.

Step3: Calculate number of vitamin B2 tablets

First, convert the RDA of vitamin B2 from g to mg. Since 1 g = 1000 mg, 0.0030 g = $0.0030\times1000=3$ mg. Each tablet has 2.0 mg. The number of tablets $n=\frac{3}{2.0}=1.5$ tablets.

Step4: Convert g to mg for selenium

Since 1 g = 1000 mg, to convert 0.000070 g to mg, we multiply by 1000. $0.000070\times1000 = 0.07$ mg

Answer:

(a) 410000 μg/day
(b) 0.9 g/day
(c) 1.5 tablets
(d) 0.07 mg/day