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Class 1 (Marathi)

Course: Class 1 (Marathi)>Unit 2

Lesson 2: What is subtraction?

Intro to subtraction

Sal talks about what it means to subtract. The examples he uses are 4-3 and 5-2. Created by Sal Khan.

Want to join the conversation?

• What if the 2 numbers were switched? How can you even go below zero?
• Below zero there would be negative numbers
• How far does negative numbers go? Is it like normal numbers? Never ending?
• Yes, Negative numbers go on forever just on the other side of the number line.
• Why subtraction has this (-) sign?
• It is easier to use the (-) sign is stead of saying plus a negative.
• Can you take away 1/2 of something?
• Depends on the item. For example, you can cut a sandwich in half and take one piece.
• So then it's possible to do negative addition?
• It is possible, because you can add a number to a negative number to make it positive or closer to 0.
(1 vote)
• who invented subtraction?
• Nobody knows but it was found in a book called Mercantile Arithmetic by Robert Recorde
• How would you represent negative numbers?
• Negative numbers represent the distance in the opposite direction on the number line. The negative symbol can be seen as a subtraction sign, because 0 - 5= -5.
• What person invented math
• No one person invented math, many people contributed to it's development over many, many years.
• how do i learn how to do more easy subtraction cuz i suck at subtraton and im super good at addition.
• so count on ur fingers so lets say the problem is 8-3 u hold up 8 fingers and then take 1 away then u would be at 7 fingers then u keep taking away fingers until u toke away 3 fingers and how many fingers you are holding up is the awnser
(1 vote)
• Is it just me or does subtraction take slightly more brain power than addition.
• I also agree that subtraction seems more difficult than addition. This is likely because we learned addition before we learned subtraction, so since we've known addition longer, it may seem easier when compared to subtraction.

Video transcript

Voiceover:Let's explore what it means to subtract numbers. So let's say that I want to figure out what 4, what 4 minus 3 is. 4 minus 3. So one way to think about this, is you start with 4 objects. And so let me just draw 4 objects. So there I have 1, 2, 3, and 4. And when I ... So this is the 4 objects right over here. And when I say minus 3, or if I'm going to subtract 3 from the 4, one way to think about it is, I'm going to take 3 of these 4 objects away. So let's do that. So I'm going to take away 1, I'm going to take away 2, and I'm going to take away 3. Notice, I took away 1, 2, 3 objects. So how many do I have leftover? Well, if I start with 4 and I take away 3, I subtract 3, 4 minus 3, I am left with, I am left with, 1 object, right over here. So 4 minus 3 is equal to, is equal to 1. Fascinating. Let's do another one of these. Let's figure out what 5, what 5, what 5 minus 2 is. And let's write it this way. Let's say we want to figure out something, some question mark, some question mark ... Actually, let me just clear this out. I'll just do it right over here, actually. So let's say we have some question mark. So there's some unknown number right over here. So I'll just put a question mark over here. And we say that unknown number is equal to, is equal to 5, 5 minus 2. Minus 2. Minus 2. So what is this going to be? Well let's visualize it. This means I have 5 things and I'm going to take away 2 of them and this is going to be what I have leftover after I start with 5 and take away 2. So I have 1, 2, 3, 4, 5 things. Now I am going to take away 2 of them. So I'm going to take away 1 and 2. So I took away 1, 2 objects. So how many do I have leftover? Well, I have leftover these, these ... Let me do this in a different color. I have leftover these purple things right over here. So how many is that? How many do I have leftover? Well, I have leftover 1, 2, 3 of my original 5. So something is equal is 5 minus 2. That something is 3. 3 is equal to 5 minus 2. Let me just replace this with a 3. So we see that 3 ... Actually, let me do the 3 in the same color as this green. So we see that 3, 3 is equal to 5 minus 2 or we could say that 5 minus 2 is equal to 3. Either way.