Video: Addition and Subtraction of Numbers up to 9

William is playing a board game. From start, he moves 10 spaces forward. In his next turn, he moves 6 spaces back. How many spaces away from START is he now?

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Video Transcript

William is playing a board game. From start, he moves 10 spaces forward. In his next turn, he moves six spaces back. How many spaces away from start is he now?

If William begins on start and he moves 10 spaces forward. On his next turn, he moves six spaces back. We want to know how many spaces is he away from start. For this unknown value, we can use the variable π‘₯. What kind of equation can we write to model the situation? We can write it a few different ways. First, William went forward 10 spaces. So, we can start with positive 10. And then, he went back six spaces. We can represent that mathematically with negative six. If you take positive 10 and subtract six, you’ll get π‘₯, the number of spaces away he is from the start. 10 minus six equals four. And that means our π‘₯-value is four.

Currently, the way it’s written: it says four equals π‘₯. But it’s fine to rearrange it in a more common way: π‘₯ equals four. 10 minus six equals π‘₯ is only one way to model this situation with an equation. We could say that π‘₯ β€” the number of spaces away from start William is β€” plus the six places backwards he walked must be equal to the 10 total forward spaces. If π‘₯ plus six equals 10, then we can solve the problem by subtracting six from both sides of the equation. π‘₯ plus six minus six equals π‘₯ plus zero, which is π‘₯, and 10 minus six equals four. Both methods show us that William is four places away from start.

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