back-of-the-envelope calculation

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back-of-the-envelope calculation

A calculation or mathematical formulation that is approximated in a quick, informal, and rough manner, as might be sketched out on a scrap of paper (such as the back of an envelope). When it came time to pay the bill, we had to do some back-of-the-envelope calculations to figure out who owed how much.
References in classic literature ?
He did not move at the sound of the door, and continued his calculations until the flash of the torches lighted up with an unwonted glare the sombre walls of his cell; then, raising his head, he perceived with astonishment the number of persons present.
Adrienne had made her calculations, as she fancied, with some attention to the ways of the world.
Is it not a beautiful spectacle--the spectacle of a century or two of inherited labour, patience, intellect, rectitude, character, perseverance, and calculation, with a stork sitting on the roof above it all?
Barbicane took the paper, and began to make his calculations with great rapidity.
And all arithmetic and calculation have to do with number?
With regard to the expense of this removal, he would say, at a rough calculation, that two or three silver tea or coffee-pots, with something additional for drink (such as a muffineer, or toast- rack), would more than cover it.
The calculations of various life assurance and annuity offices, among other figures which cannot go wrong, have established the fact.
Sometimes a magnate addressed him, to turn the stream of his own particular discussion towards him; but Mr Merdle seldom gave much attention to it, or did more than rouse himself from his calculations and pass the wine.
No sooner had this little plan shaped itself in his mind than he began to be busy with exact calculations about the wood to be bought and the particular article of furniture that should be undertaken first--a kitchen cupboard of his own contrivance, with such an ingenious arrangement of sliding-doors and bolts, such convenient nooks for stowing household provender, and such a symmetrical result to the eye, that every good housewife would be in raptures with it, and fall through all the gradations of melancholy longing till her husband promised to buy it for her.
When he had effected this proper restitution, "Now," said he to himself, "let us inhale much maternal air, much freedom from cares, much health, let us allow the horse Zephyr, whose flanks puff as if he had to respire an atmosphere to breathe, and let us be very ingenious in our little calculations.
Xavier returned from I do not know where at midnight, absorbed in calculations on the eternal question of his Aurora--la belle Aurore, whom I begin to hate.
He remained absorbed in his own reflections, giving himself up to secret calculations, passing his nights among heaps of figures, and making experiments with the strangest-looking machinery, inexplicable to everybody but himself.
Once when making such calculations he wrote down his own name in French, Comte Pierre Besouhoff, but the sum of the numbers did not come right.
I can be making some calculations with reference to the number of hospital beds for each transport.
But for Rosa and William, the calculations of the envious neighbour would have been correct.