Whenever you write down a two-digit number, reverse the digits, and subtract one from the other, the result will always be divisible by 9.

Why: Any two-digit number  can be written as 10T + U , where T is the tens digit and U is the units digit. Reversing the digits gives the number 10U + T, and subtracting the second from the first yields 10T+ U - (10T-U) = 9T-9 U=9(T-U), which is clearly divisible by 9.

#fact  #math  
∞  02/01/10
61 notes
  1. samtwamz reblogged this from lilouette
  2. iamyourcreeper reblogged this from hidinginthenight and added:
    I think so, but very nice, spoon
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  4. hidinginthenight reblogged this from fuckyeahmath and added:
    99 -> 99 -> 99-99=0 Does zero count?
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