destroyer

[hye340]

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A bowl contains 1000 tickets numbered, between 1 and 1000. What is the probability that a number is between 10 and 90?
I don't get why its 81/1000?
thanks

 

[clutchfans]

90-10=80
+1 to include 10, thus you have 81

 

[qkrdpsk]

90-10=80
80+1=81 (+1 since 10 & 90 are inclusive)

 

[SDDDAT]

A bowl contains 1000 tickets numbered, between 1 and 1000. What is the probability that a number is between 10 and 90?
I don't get why its 81/1000?
thanks

Yea I was confused about the answer too until I realized that when it asks for numbers between 10 and 90, it's actually asking for numbers between and including 10 and 90.

 

[hye340]

why can't it be 82 then 90-10=80 then +2 for 10 and 90

 

[SDDDAT]

why can't it be 82 then 90-10=80 then +2 for 10 and 90

When you do 90-80, you're also including 90. It's easier to see it if say you do 3-1=2. The 2 includes 2 and 3 but not 1.

 

[qkrdpsk]

tbh idk the explanation.. i just memorized the formulas for the test lol

maybe this link will help you see why you have to +1 & not 2:
http://mathcountsnotes.blogspot.com/2012/05/how-many-numbers-terms-space-inclusive.html?m=1

 

[qwrupae]

good,It's easier to see it if say you do 3-1=2. The 2 includes 2 and 3 but not 1.