<p>Fifty percent of the people alive today (have) never made a phone call, (but) thirty percent (still) have no electricity connections to (their) homes. No error.</p>
<p>I thought "have" and "their" are wrong because they should be singular, since the subject refers to a quantity/amount and answers the question "how much?". We say: "twenty percent of the class is going to fail the test". So, "have" should be "has", and "their" should be "its"???</p>
<p>The answer is "but", because it makes an illogical transition between the clauses. </p>
<p>Are all three wrong? Or can phrases referring to measurement, quantity/amount be flexible like collective nouns, meaning you can use the plural form and the singular form? For collective nouns, it depends on how you refer to them---as discrete entities or as a single unit.</p>
<p>Thanks in advance.</p>