Solutions Wanted

BBird

1.300 people who suffer from A, B and C diseases. People suffering from A disease take 35%, People suffering from B take 45% and people suffering from C take 40%. People who suffer from two of the diseases take 10%. How many people who suffer from only one disease?

2.A rectangle inscribed inside a circle that has a radius of 3. If the rectangle is not a square, what range can the rectangle’s circumference be?   

3.There are 4 balls with colors in red, white, blue and green separately. If 2 balls are taken out. What is the probability of green ball or blue ball?

4.4 numbers are taken out from 0—9 as telephone numbers. If the first digit of the four-digit telephone number cannot be 0, how many telephone numbers can we have from these numbers?  


Thanks!

iamf

1、If x persons have 3 diseases, and y persons have only 1 diseases, we get:
x+y+10%*300=300
3x+10%*300*2+y=(45%+40%+35%)*300

The solution of the previous equations is: x=15, y=255

so the answer of your question is 255.

2.we suppose the length and width of the rectangle is x,y respectively, then x^2+y^2=6^2=36.

the question is what range is the value of 2x+2y.

(x+y)^2< 2(x^2+y^2) if x does not equal to y
(x+y)^2>4xy if x does not equal to y

Thus 2(x+y)< 12根号2
but i can not solve ">"

3.题意不清

4. 9*10*10*10=9000

joywzy

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