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分數轉成小數 (例子1 英語) : 分數轉成小數 (例子1)
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- Lets see if we can express 16 over 21 as an decimal
- Or we can call this sixteen twenty first.
- This is also sixteen divided by 21.
- So we can literally just divide 21 into 16.
- And because 21 is larger than 16,
- we're going to get something less than 1.
- So let's just literally divide 21 into 16.
- And we we're going to have some less than one, so lets add some decimal places here.
- We're going to round to the nearest thousandths in case our digits just keep going on and on and on.
- And let's start dividing, 21 goes into 1 zero times,
- 21 goes into 16 zero times.
- 21 goes into 160, well, 20 would go into 160 8 times,
- So let's try 7, lets see if 7 is the right thing.
- 7 times 1 is 7, 7 times 2 is 14 and then when we subtract,
- we should get a remainder less than 21.
- If we picked the largest number here that goes into the largest number here,
- that if I multiply it by 21 I get close to 160 without going over.
- And so if we subtract we do get 13, we do get 13.
- So that worked, 13 is less than 21.
- And you could just subtract, I did it in my head right there,
- but you could re-group, you could say that this is a 10
- and then this would be a 5
- 10 minus 7 is 3.
- 5 minus 4 is 1,
- 1 minus 1 is zero.
- Now lets bring down a zero
- 21 goes into 130, so lets see, would 6 work?
- It looks like 6 would work
- 6 times 21 is 126, so that looks like it works.
- So lets put a 6 there
- 6 times 1 is 6
- 6 times 2 is 120. There's a little bit of an art to this.
- Alright, now let's subtract.
- Once again, we can regroup,
- this would be a 10, we've taken 10 from
- essentially this 30, so this becomes a 2
- 10 minus six is 4
- 2 minus 2 is zero
- 1 minus 1 is zero.
- Now let's bring down, now lets bring down another zero
- 21 goes into 40, well, almost 2 times
- but not quite, so only 1 time.
- 1 times 21 is 21, and now lets subtract
- This is a 10, this becomes a 3.
- 10 minus 1 is 9
- 3 minus 2 is 1 and we're going to have get
- this digit because we want to round to the nearest thousand.
- So if this is 5 or over we're going to round up
- if this is less than 5 we're going to round down.
- So let's bring another 0, lets bring another
- lets bring another zero down here
- and 21 goes into 190, lets see I think 9 will work
- Lets try 9, 9 times 1 is 9
- 9 times 2 is 18, when you subtract 190 minus 189 is 1
- And we could keep going on and on but we already have
- enough digits to round to the nearest thousand.
- This digit right over here is greater than
- this is greater than or equal to 5, so we will round up
- in the thousandths place.
- So if we round to the nearest thousandths,
- we can say that this is 0.76
- and then this where we're going to round up, 762.
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