Dogs are twice as fast as people. A man walks half way, but a dog walks the whole way.
That is to say, people walk all the way, and dogs walk all the way, namely:
200X2=400 meters
Calculation rules of multiplication:
Number alignment, starting from the right, multiply the first factor by the number on each bit of the second factor, and the end of the number will be aligned with which bit of the second factor.
When the number of digits of the multiplicand satisfies 7, 8 and 9, the method is as follows:
It is 9: base minus complement-times, low plus complement once.
The multiplicand is 8: the basic complement is subtracted once, and the low complement is added twice.
It's 7: the base MINUS the complement once, and the lower limit plus the complement three times.
For example: 987x879 = 867573 (the complement of 879 is 12 1). Order: The multiplicand subtracts 12 1 from the number 7, and adds 363 to the lower order to get 98-6 153. The multiplicand-+bit 8 subtracts 12 1, and the low bit adds 242 to get 9-76473. Subtract 12 1 from the base of the multiplicand and add 12 1 to get 867573 (product).