When dealing with base 10 representations, multiplying by 10 is a simple matter of adding zeroes;
dividing numbers that end with a zero by two is (usually) an afterthought;
doing both operations in that sequence is (usually) equally trivial, the only effortful thing I have to do is adding or subtracting a multiplicand, once or twice or thrice.
It’s not easier than having the result imprinted in my memory, but it cuts away ~ three quarters of the table.
What? How is multiplying by 5 more convenient than any other number?
When dealing with base 10 representations, multiplying by 10 is a simple matter of adding zeroes;
dividing numbers that end with a zero by two is (usually) an afterthought;
doing both operations in that sequence is (usually) equally trivial, the only effortful thing I have to do is adding or subtracting a multiplicand, once or twice or thrice.
It’s not easier than having the result imprinted in my memory, but it cuts away ~ three quarters of the table.