Mary has Taxable Income for the current year of $425,000, of which $216,000 is spent on goods and services that are subject to GST at a rate of 5 percent.

Her sister, Joan, is a part-time student living in the same province and has Taxable Income of $18,000. During the current year, as a result of using some of her savings, she spends $22,400 on goods and services that are all subject to GST.

Determine the effective GST rate as a percentage of the income of the two sisters.