Of the citizens who disapprove of the prime minister's overall job performance, most disapprove because of the prime minister's support for increasing the income tax.
Conclusion (So)
Theresa probably approves of the prime minister's overall job performance.
Evidence
Most people who disapprove of the PM's performance do so because of the PM's support for increasing the income tax.
But, Theresa believes that the income tax should be increased.
Evaluate
Because of the symbol repetition in this argument (theresa / income tax / prime minister are all mentioned twice) and because of the quantifier most, this argument seems like a good contender for turning into an algebraic recipe.
Prem 1: Most people who are X are Y (X = disapprove of PM, Y = don't want income tax increased)
Prem 2: Person A is not Y. (A = Theresa)
Conc: Person A is probably not X.
Conversationally, we could say that . We don't know whether most people who support the tax support the PM .
There could be 100 people, 98 of whom oppose the PM. Most of those 98 oppose the PM because of the increased tax. So let's say 60 of the 98 oppose the PM because of the increased tax. That leaves 38 people who oppose the PM, but not because of the tax. And 2 people who support the PM.
If we know that Theresa is not opposed to the tax, does that mean she's more likely to be one of the 2 people who support the PM or the 38 people who oppose the PM for some reason other than the tax?
Numerically, the latter is more probable.
Goal
The conversational objection is harder to deal with, so we should probably look for our algebraic structure:
P1: Most people who are X are Y. P2: Person A is not Y. C: Person A is probably not X.