@[email protected] to Lemmy [email protected] • 1 year agoPaniki.postimg.ccmessage-square145fedilinkarrow-up11.28K
arrow-up11.23KimagePaniki.postimg.cc@[email protected] to Lemmy [email protected] • 1 year agomessage-square145fedilink
minus-square@[email protected]linkfedilink3•edit-21 year agoBut what about 14, 21 and 28? 14 - 4*2 = 6, not divisible by 7 21 - 1*2 = 19, not divisible by 7 28 - 8*2 = 12, not divisible by 7 Or did I misunderstand the algorithm? EDIT: I didn’t realize that you remove the last digit when subtracting, got corrected in the replies.
minus-square@ColalextrastlinkEnglish7•edit-21 year agoIt goes like this create 2 distinct numbers by isolating the last digit from the other. For example, 154 becomes 15 and 4. double the number derived from the last digit. So, the four becomes 8. subtract from the number derived from the preceeding digits. 15 - 8. the resulting number is 7. Seven is divisible by 7, so we know 154 is divisible by 7.
minus-square@[email protected]linkfedilink1•1 year agoOooh, I didn’t realize that you subtract from the original number without the last digit. Thanks
minus-square@[email protected]linkfedilink4•edit-21 year agoYeah you got it wrong, it’s 1 - 4*2 = -7 2 - 1*2 = 0 2 - 8*2 = -14
But what about 14, 21 and 28?14 - 4*2 = 6, not divisible by 721 - 1*2 = 19, not divisible by 728 - 8*2 = 12, not divisible by 7Or did I misunderstand the algorithm?EDIT: I didn’t realize that you remove the last digit when subtracting, got corrected in the replies.
It goes like this
create 2 distinct numbers by isolating the last digit from the other. For example, 154 becomes 15 and 4.
double the number derived from the last digit. So, the four becomes 8.
subtract from the number derived from the preceeding digits. 15 - 8.
the resulting number is 7. Seven is divisible by 7, so we know 154 is divisible by 7.
Oooh, I didn’t realize that you subtract from the original number without the last digit. Thanks
Yeah you got it wrong, it’s
1 - 4*2 = -7
2 - 1*2 = 0
2 - 8*2 = -14