The swimming pool is 50 meters long. To swim 1 km, you have to swim 20 such lengths. Because 1 km (1000 m) contains as many 50 m, this (50 m) has the same length. So 1000÷50=20 (pieces).

Considering that division and multiplication are reciprocal operations, the meaning of multiplication is a simple operation to find the sum of multiple identical addends. This situation can also be interpreted as: the divisor subtracts the divisor until the remainder value is lower than the divisor.

About "0 is inseparable"

According to the meaning of division, division is the operation of finding the other factor by knowing the product of two factors and one of them. According to the reciprocal relationship between division and multiplication, if the divisor is 0, then:

(1) When the dividend is not 0 (for example, 3÷0), because "any number multiplied by 0 is equal to 0 and cannot be equal to a number that is not 0 (for example, 3)", the quotient of the division formula does not exist at this time-that is, 0 times of any number cannot be non-zero.

(2) When the dividend is 0, that is, the division formula is 0÷0, because "any number multiplied by 0 equals 0", the quotient can be any number-that is, 0 times of any number equals 0.

In order to avoid the above two situations, it is mathematically stipulated that "0 cannot be divided".