http://www.cut-the-knot.org/WhatIs/WhatIsArithmetic.shtml [2]
http://www.math.com/students/practice/arithmeticpractice.htm [3]
http://www.mathtutor.ac.uk/arithmetic [4]
Links[1] https://hootsgo.org/?q=node/6729 [2] http://www.cut-the-knot.org/WhatIs/WhatIsArithmetic.shtml [3] http://www.math.com/students/practice/arithmeticpractice.htm [4] http://www.mathtutor.ac.uk/arithmetic
