Today's abstract
Let's talk about impossible multiplication. An impossible multiplication is just it doesn't make any sense.
``How much is 6 Euro pasta for 5 people?''
is 6 * 5 = 30 Euro. But,
``How much is 6 Euro pasta for 7 Euro salad?''
doesn't make any sense. If someone does 6 * 7 = 42. What does it mean? But it seems some people teach these stuffs to children. They make the students to hate mathematics. That's pity.

Main part
Here multiplication is only with a number. If we have some variables x and y, we can do 3 * x + 5 * y, but not x * y. You might wonder what kind of mathematics we can not do x * y, that is such a simple operation. But I would like to emphasize, we have not so much freedom to compute numbers in real world with meaning. We all learned that we sometimes can not multiply numbers, again in real world.
Let's think about in a restaurant as an example. For instance, x or y are a menu A and B's price, respectively. As more vivid …
Let's talk about impossible multiplication. An impossible multiplication is just it doesn't make any sense.
``How much is 6 Euro pasta for 5 people?''
is 6 * 5 = 30 Euro. But,
``How much is 6 Euro pasta for 7 Euro salad?''
doesn't make any sense. If someone does 6 * 7 = 42. What does it mean? But it seems some people teach these stuffs to children. They make the students to hate mathematics. That's pity.

Main part
Here multiplication is only with a number. If we have some variables x and y, we can do 3 * x + 5 * y, but not x * y. You might wonder what kind of mathematics we can not do x * y, that is such a simple operation. But I would like to emphasize, we have not so much freedom to compute numbers in real world with meaning. We all learned that we sometimes can not multiply numbers, again in real world.
Let's think about in a restaurant as an example. For instance, x or y are a menu A and B's price, respectively. As more vivid …