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> Most notably it requires understanding that in 3+4 you start at 3 and move 4 spaces to the right. In 3x4 you start at 0 and move to the right 3 spaces 4 times

by ajuc 5y ago

> Most notably it requires understanding that in 3+4 you start at 3 and move 4 spaces to the right. In 3x4 you start at 0 and move to the right 3 spaces 4 times. That's a weird way to describe it. Doesn't make it more understandeable and isn't useful for solving problems. So why bother? We were taught the definition of multiplication (it's just repeating addition). So if you have 3+4 it's starting at 0 then jumping by 3 and then jumping by 4. If you have 3*4 it's the same as 4+4+4 which is starting at 0 and jumping by 4 three times. Or vice versa. I don't think we had that jumping on number line on that lesson, probably not since it's kinda obvious and provides little value when you know the definition. We had a lot of word problems and whoever was the fastest would explain how to solve it to others. So basically somebody was the first to realize you don't need to do 2+2+2+2+2+2 when you can calculate the solution as 6+6. Kid got reputation boost for being smart in front of others and others stole the technique to be the fastest the next time. This got me into math.

spywaregorilla 5y ago
That is entirely the point. The number line is awkward for multiplication. But mapping the relationship between multiplication and the area of rectangles is very visually intuitive. Geometric reasoning is powerful. Being able to use your understanding of multiplication rules to derive the formula for the volume of a cube, or a cylinder, or whatever is probably more insightful than realizing some arithmetic tricks.
- raegis 5y ago
  > That is entirely the point. The number line is awkward for multiplication. Strong disagree. The number line is one of the best tools for understanding multiplication of numbers (not just whole numbers, but any decimal). The problem is that it is no longer taught. Example: American rulers have both metric (cm) and Imperial (inch) units. You can use it to visually multiply and divide by 2.54. To generalize multiplying positive numbers x and y, (1) Mark x on a number line, (2) create another number line with the number 1 placed where x would be on the original line, (3) find y on the new number line, and (4) the corresponding point on the original line is the product x*y. The point: Multiplication is scaling (stretching, shrinking, whatever you want to call it). The Common Core tries to address this.

by ajuc 5y ago

spywaregorilla 5y ago

That is entirely the point. The number line is awkward for multiplication. But mapping the relationship between multiplication and the area of rectangles is very visually intuitive. Geometric reasoning is powerful. Being able to use your understanding of multiplication rules to derive the formula for the volume of a cube, or a cylinder, or whatever is probably more insightful than realizing some arithmetic tricks.

raegis 5y ago
> That is entirely the point. The number line is awkward for multiplication. Strong disagree. The number line is one of the best tools for understanding multiplication of numbers (not just whole numbers, but any decimal). The problem is that it is no longer taught. Example: American rulers have both metric (cm) and Imperial (inch) units. You can use it to visually multiply and divide by 2.54. To generalize multiplying positive numbers x and y, (1) Mark x on a number line, (2) create another number line with the number 1 placed where x would be on the original line, (3) find y on the new number line, and (4) the corresponding point on the original line is the product x*y. The point: Multiplication is scaling (stretching, shrinking, whatever you want to call it). The Common Core tries to address this.