Reader question:

What does the expression "you do the math" mean? What math? Give examples.

My comments:

"You do the math" is a colloquial¹ expression that usually comes at the end of an argument as emphasis, emphasizing on an advantage or disadvantage of a point.

Usually, a string of figures are given before you're asked to "do the math", that is, to do your own calculations and reach the conclusion that has just been suggested.

Sometimes no real arithmetic is involved. For example, 20 years ago, the majority of Chinese students in America chose to stay after completing their academic studies. Nowadays, most of them come back. Why is that? The reason is obvious. Two decades ago, people stayed in America to achieve an American Dream embodied² by a car and a house of their own. Now, that (part of the) American Dream is just as easy of accomplishment³ here in China, if not easier. Plus, the home country gives the extra comfort of, well, being home – they don't have to feel homesick all the time. Chinese being Chinese, spiritually they are always close to their roots. You do the math – Little wonder those students are turning homeward en masse.

Here are a few media examples:

1. Vista⁴ Sales – You Do the Math

Despite Gates bragging⁵, Vista sales still don't add up to 50 percent of all the new PCs sold in 2007.

- internetnews.com, January 8, 2008.

2. You do the math (at the end of birthday parties)

And in the end, who cares? We need not abandon the idea of parties in restaurants altogether. After all, not everyone has the space, the culinary skill or the energy to celebrate friends in the style they deserve. But perhaps there should be a few rules of order(ing). First, avoid long tablefuls of too many people, lest the honoree feel like she is presiding over the Last Supper. "Groups of 10 or under are great," said a novelist who's still recovering from a raucous⁶ gathering⁷ at a West Village restaurant attended by 19 of her nearest and dearest. If it's a fancy place, consider limiting the menu choices ahead of time to several reasonably priced alternatives and house wines, perhaps to be printed on a keepsake placard. If you have piles of money, consider paying for everybody. If you don't, consider disclosing a rough price of entry ahead of time. And if that is exceeded, suck it up, because the alternative is just unpleasant.

- nytimes.com, May 6, 2007

3. A depressing day? You do the math

Today is the most depressing day of the year, and not just for those federal election candidates who will be losers by day's end.

So says Cliff Arnall, a health psychologist at the University of Cardiff in Wales who came up with a formula - 1/8W+(D-d)3/8xTQMxNA - to calculate the lowest emotional point of the year. He did this at the request of the travel industry, which wanted to know the best day in January to book a summer holiday.

Seems people tend to make travel plans when they're at their lowest, to give them something to look forward to.

Arnall factored in the dreariness⁸ of the (W)eather, the arrival of maxed-out Christmas bills or (D)ebt, minus monthly salary (d), (T)ime elapsed since Christmas and the failure to keep a New Year's resolution or to (Q)uit a bad habit, low (M)otivational levels and the need to take action (NA). He came up with January 24, or the Monday closest to January 24, since Monday is the most disliked day of the week.