Which of the following sentences is correct?
- The monthly income of households in the first and tenth groups differed by HK$101,230.
- The monthly incomes of households in the first and tenth groups differed by HK$101,230.
The sentence means that the monthly income of the first group and that of the tenth group differed by HK$101,230. It seems to me that the 2 is correct because "differ" does not make sense when the subject is singular i.e. "A differs by $10" does not make sense while "A and B differ by $10" makes sense.
Moreover, which of the following sentences is correct?
- Compare the income of the same group in 2006 and 2016
- Compare the incomes of the same group in 2006 and 2016
The sentence asks to compare the income of a group in 2006 and that of the same group in 2016. Thank you.