Snow White and the seven dwarfs. Heigh -ho. Heigh-ho, it’s off to work we go. Seven is a prime number but you’ll need to work to figure out if a number is divisible by seven.
Here is the rule, take the last digit in a number. (a) Double that number then (b)subtract the doubled number from the rest of the digits. (c) If that number is divisible by seven then the entire number is divisible by seven.
For example, 672: a) 2*2=4 b) 67-4=63 c) 63/9=7 okay
357: a) 7*2=14 b) 35-14=21 c) 21/3=7 okay
This is a technique you’ll need if you’re ever stuck on a deserted island in the middle of some ocean, if there a thermonuclear holocaust which wipes out civilization as we know it or if you are taking a manual math test. Otherwise, since you live in the 21st Century, just use a calculator.
Schneewitchen und die sieben Zwerge posted by lemmatt:
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