In the case of one movie-rental chain, the answer is: add pizza.

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The obvious answer is to add an external antenna.

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So far the debate has focused on what a potential number two can add to a ticket (with the general answer being, not much).

ECONOMIST: Be my number two

The answer is, it would add at most 4% to the cost of building an iPhone.

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When I asked the FSA if they had seen emails from Mr Tucker they said they could not add anything, or answer questions about anything not in the document, as a wider FSA investigation is ongoing.

BBC: The strange silence and an absence of information

Add to this the 12% that did not answer this set of questions, and a full 86% of small businesses are not expressing concerns over borrowing.

FORBES: Small Businesses Don't Need Loans, They Need Business

"What I'm saying is that they've got it very wrong in the past and that qualifications must be made to count" came the answer from Andrew RT Davies which doesn't add up to "yes".

BBC: Welsh Baccalaureate or bust?

The official gave a long and evasive answer, which seemed to add up to no.

NEWYORKER: The Next Crusade

The assembly government said Dr Gibbons did not have anything further to add to that answer.

BBC: NEWS | UK | Wales | Mid | Cuts claim over heart unit cash

Add in the sovereign debt problems affecting Greece, Portugal and Spain and it becomes clear that the answer to when is not soon.

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But the authors have taken pains to answer those quibbles, and they disclose their sources so that readers can add or subtract as they see fit.

ECONOMIST: Invading Iraq