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A microbiologist has 1,256 microbes growing in culture.
When he checks again after fifteen minutes, there are
2,283 microbes in the same culture, so they're growing
pretty fast. Estimate the difference between the number
of microbes at each check by rounding each number to the
nearest ten.
So what they want us to do, they want us to round each
number to the nearest ten, and then with the rounded numbers,
find the difference between the two checks.
So let's round each of these numbers.
So we started with 1,256 microbes.
So how do we round this to the nearest ten?
That's what they want us to do.
So you look at the tens place.
The tens place is that 5 right there.
So if we round it up, it would go to a 6.
If we round it down, it would stay at a 5.
If we round it up, this would be 60.
If we round it down, this will be 50.
And the rule for rounding is you look at the place one
below that.
You go to the ones place in this case, and you see if that
is 5 or more, or 5 or greater, and it is.
It's 6, which is definitely 5 or greater, so we
want to round up.
So we want to round up, and we're rounding up to the
nearest ten.
So this will be go from 56 to 60, so it'll be 1,260.
We've rounded up.
Now, when we wait fifteen minutes, we check and we see
that there are 2,283 microbes.
Once again, let's look at the tens place.
That's the 8 right there.
Let me do that in a different color.
That is the 8 right there.
And you look at the place one below that.
If that's 5 or greater, you round up.
Otherwise, you round down.
This right here, 3 is less than 5 so you
want to round down.
We want to round down, so we're going to be left with
2,200, and instead of 83, we're just going to have 80.
2,280.
Now, they want us to estimate the difference between the
number of microbes at each check by rounding each number
to the nearest ten, so we've done that part.
We've rounded each number to the nearest ten.
Now we have to find the difference.
So let's subtract the first check from the second check.
That's how we get a positive number.
So let's do that.
So if we subtract this 1,260-- let me just copy and paste it.
So we want to subtract this-- copy it and paste it.
We want to subtract that from the 2,280 to figure out the
difference.
So we're going to subtract here.
Let me put the subtraction sign, and let's do some
subtraction.
So you go first to the ones place.
0 minus 0.
Well, that's just going to be 0.
8 minus 6 in the tens place, it's really 80 minus 60.
That's going to be 2, but since it's in the tens place,
it's 20, or you could just do 80 minus 60 is 20, so
everything makes sense so far.
2 minus 2 is 0, and then 2 minus 1 is 1.
So when we rounded each number to the nearest ten and then
took the difference, our estimated difference is 1,020.