the kilopascal is a unit of measure for atmospheric pressure. suppose the atmospheric air pressure at sea level is about 103 kilopascals. for every 1000-m increase in altitude, the pressure decreases about 11.1%. what is the approximate pressure at an altitude of 3000m?
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Apparently the answer is 72, but how do I get 72?

Question

the kilopascal is a unit of measure for atmospheric pressure. suppose the atmospheric air pressure at sea level is about 103 kilopascals. for every 1000-m increase in altitude, the pressure decreases about 11.1%. what is the approximate pressure at an altitude of 3000m?
....
Apparently the answer is 72, but how do I get 72?

ganeshie8 · Answer

`pressure decreases by 11.1% for every 1000 m increase in altitude`

that means, pressure drops to 100-11.1 = 88.9% for every 1 km increase in altitude, yes ?

ganeshie8 · Answer

what is 88.9% of 103 ?

anonymous · Answer

where did you get 100 from?

ganeshie8 · Answer

that is a very good question !

ganeshie8 · Answer

before answering that, let me ask you a small question

ganeshie8 · Answer

suppose there are 100 students in your class and 11 of them are wearing red dress.

here is the question : how many students are "not" wearing red dress ?

anonymous · Answer

89

ganeshie8 · Answer

Excellent!

ganeshie8 · Answer

cent means 100

percent means per 100

ganeshie8 · Answer

11% means 11 per every 100

asib1214 · Answer

or every 100

ganeshie8 · Answer

`pressure decreases by 11.1% for every 1000 m increase in altitude`

ganeshie8 · Answer

if 11.1% of pressure is lost, how much is still there  ?

anonymous · Answer

from 100 or 1000?

ganeshie8 · Answer

percent always refers to 100

anonymous · Answer

88.9

ganeshie8 · Answer

So you do see that the pressure reduces to 88.9% for every 1000 m increase in altitude

ganeshie8 · Answer

Since the pressure is 103 at sea level, it should be 88.9% of 103 at a height of 1000m

ganeshie8 · Answer

what is 88.9% of 103 ?

anonymous · Answer

9156.7? "of" means multiplication, right?

asib1214 · Answer

91.56

anonymous · Answer

how did you get 91.56

asib1214 · Answer

88.9/100 X 103KPa

anonymous · Answer

i multiplied 88.9 and 103 together, and i got 9156.7

ganeshie8 · Answer

"of" means "multiplication" 

yes

asib1214 · Answer

as ganshie said, it's 88.9% "percent" and percent means out of 100. 
or 88.9/100

ganeshie8 · Answer

but calculating percentages is a bit tricky, you need to think a bit...
 simply multiplying two numbers doesn't give you the percent

ganeshie8 · Answer

I suggest you watch this quick video first https://www.khanacademy.org/math/pre-algebra/decimals-pre-alg/percent-intro-pre-alg/v/finding-percentages-example

anonymous · Answer

oh wait, isn't there the rule with moving the decimal two places to the.. right? or left? or maybe thats for something else

asib1214 · Answer

ganshie before you go....|dw:1450334114131:dw|