Matthew takes two 50-milligram iron tablets each day. how many
grams of iron does he take daily?

Given –  

Mg of iron tablets consumed = 50 mg

Number of tablets consumed = 2

So,

Total mg of iron tablets consumed = 2 X 50 mg

                                                          = 100 mg

Total grams (g) of iron tablets consumed = 100 X 0.001 g

Because  1 mg = 0.001 g

So,

Total grams of iron tablets consumed would be 0.1 grams.