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added 11 characters in body

edited Dec 19, 2017 at 8:55

edited Dec 19, 2017 at 8:55

Ruby, 7169 bytes

->a,b{(0..a+ba+b=~/$/).all?{|r|(0..r).sum{|w|a/10**w%10*(b/10**(r|w|a[w].to_i*b[r-w)%10)w].to_i}<10}}

->a,b{(0..a+b).all?{|r|(0..r).sum{|w|a/10**w%10*(b/10**(r-w)%10)}<10}}

->a,b{(0..a+b=~/$/).all?{|r|(0..r).sum{|w|a[w].to_i*b[r-w].to_i}<10}}

answered Dec 19, 2017 at 8:46

answered Dec 19, 2017 at 8:46

 ->a,b{(0..a+b).all?{|r|(0..r).sum{|w|a/10**w%10*(b/10**(r-w)%10)}<10}}