cook

507. D .4
509. "if the sign is 3 centimeters long" - what does this mean?
     1.a+2r=3, a=2r--> r=3/4, a=3/2  then Volum=(3/2)^3+4*3/2*Pai*(3/4)^2/2  
                                               =3.375+1.6875Pai
     2. ...
Anyway, the question I can't understand. In addition," 3 centimeter",whcih I guess should be 3 meter.

510: C
541: E

Can u check our answer/ thanks!

cook

507. sorry should be 5. According to context, 7 for each since equal number and total number of 21, First, 1 each color for each group.then go blue color, green , ans the last to distribute red.
  R   R      R   9-3=6
  B   B      B   7-3=4
  G   G      G   5-3=2
  4B 2G+2R  (6-2)R
Total
  7   7      7
So, the number of maximum red = ( 6-2)+1=5
509. Method: 50^2*3 + Pai*1/2*(50/2)^2*3*4 = 3750pi+7500 --> C
510. Are u sure?  My way goes like this:
(2) x, 2x, 3*2x  if 3*2x=2 --> x=1/3
Can u check it again? thanks!