318 is the closest you'll get with multiples of 19.
19*10 = 190
19*20 = 380 which is too much.
19*15 = 190 + 19*5 = 190 + 95 = 285
19*16 = 285 + 19 = 299
19*17 = 299 + 19 - 318
Which leaves a remainer of 3.
Not sure if that's the method the book wants you to use, but that's how I'd rationalize it.
English
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Edited by Saturn: 6/20/2013 7:57:03 AMAnyway, based on the books answer you got it wrong.
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I gave an example in reply to A ToplessZombie.