The ratio of the areas of two circles is 9 to 16. If the circumference of the larger circle is 20 cm, what is teh circumference of the smaller circle?

Question

anonymous · Answer

Are you familiar with cross multiplying?  I belive you go                            9/16   times   (x/20cm)    From there, working it out it becomes (20x9)/16   and that gave me 45/4cm or 11.25

anonymous · Answer

so answer is 11.25 cm?

anonymous · Answer

yeah thats what I got, still though do you know how to cross multiply?

anonymous · Answer

yes i noe, y?

anonymous · Answer

makes life much easier, just making sure because thats usuallly all you do when you have a ratio problem like this

anonymous · Answer

ok, but i just realized that the ratio given about the two circles is their area, not circumference!

anonymous · Answer

area=pi*r*r
circumference is pi*2*r
ratio of area of circle 1 to circle 2 is 9:16.
9/16=area1/area2=pi*r1*r1/pi*r2*r2=r1*r1/r2*r2=3*3/4*4
so, ratio of r is 3:4

anonymous · Answer

is teh answer 11.25 still correct then?

anonymous · Answer

lyam, sdo wat's the final answer?

anonymous · Answer

nope
3/4=X/20
4X=60
X=60/4=15 I think

anonymous · Answer

sorry i type slow