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Scientific notation word problem: red blood cells

Vampires and math students want to know: How many red blood cells are in the a human body? We can find the answer using scientific notation. Created by Sal Khan.

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• Why was 1/10^-14 the same as 10^14? Not quite sure.
• Well, you can think it as (1/10)^-14. Then, according to the rule (a/b)^c = ((a^c)/(b^c)), you can use the distributive property:

((1^-14)/(10^-14)
When a fraction has either a numerator or denominator or both with a negative exponent, you need to switch the position. Meaning the numerator with a negative exponent would switch to the denominator for a positive exponent, and vice versa.
((1^-14)/(10^-14)) = ((10^14)/(1^14))
And since we know that 1 with a positive exponent is still one, it becomes:
(10^14)/1
And since division by one means the quotient is the dividend, it becomes:
10^14
• At in the video, you start to mention that 90 isn't in scientific notation because it isn't less than ten, which I agree with, but under that understanding, wouldn't 10^-15 technically not be in sci.n. because it isn't less than ten?
• 90 isn't in scientific notation because the coefficient isn't less than 10. Since 90 is just a number, 90 is the coefficient which isn't less than 10.

With 10^-15, the coefficient is 1 which is less than 10.

However, it should be noted that to be in scientific notation, the coefficient must also be greater than or equal to 1.

I hope this clarifies what Sal meant!
• At , Sal wrote "5 (liters) x 40%". Can someone show me how to work this out? ( You don't have to include the liters)
• this is old
also how did he get the ten to turn into a nine that is some weird math right there. Does he have anymore things involving this kind of math because i still need to understand more.
• I realize I am the only person having trouble understanding this, but why did we divide by volume of 1 red blood cell rather than multiplying? total volume of 1 red cell/ volume of 1 cell = # of blood cells??

I understand the calculation itself just confused on the formula
• At , I don't understand why you wouldn't just divide 9 into 2 and have the quotient of 0.22 there instead of "borrowing" the 10.
I calculated 0.22*10^14 which would simplify to 2.2*10^13
So i would have gotten it wrong unless i "borrowed" the 10 during my calculation.
• 0.22 x 10^14 is numerically correct, but it isn't valid scientific notation. A number which is written in scientific notation must have the mantissa (the bit before the power of ten) greater than or equal to 1, and less than 10. Here, 0.22 is not greater than or equal to 1, so it fails that test. So although 0.22 x 10^14 = 2.2 x 10^13, only the latter is correct scientific notation.
• At in the video, couldn't Sal have done 2/9 first, then made it into scientific notation, rather then multiplying it by ten? I'm kind of confused, whether I'm doing it right or wrong. Does both ways always work?
• In this video you added, you said to add 10^1 to 10^-15. The first time yo wrote it, you said it would be 10^-14. But the last few times you wrote it, you said 10^14. I thought it is still to be 10^-14. Why did you do that?
• I think he did that because the conclusion gives more understanding in that format in the overall scheme of things