Alan has given a proof for the 7* one here ![]()
For seven:
Take the last digit, double it, and subtract it from the rest of the number. If the answer is divisible by 7 (including 0), then the number is also divisible by 7:
861:86-1x2=84
84/7=12
http://web2.0calc.com/questions/prime-factorization-of-624
Thanks Alan and thejamesmachine ![]()
I'll add this to out sticky notes Reference material under "Determining factors of a large number"
@@ End of Day Wrap Sat 30/5/15 Sydney, Australia Time 11:36pm ♪ ♫
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Today our great answers were supplied by DarkBlaze347, DragonLance, CPhill, Thejamesmachine, MathsGod1, Heureka, Alan, asinus, MathsGod1 Civonamzuk and Josh4444. Thank you ![]()
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FTJ means 'For the juniors'
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