IMOmarmar29 wrote:hi all
an archery target has 3 concentric regions. the daimeter of the regions are in the ratio 1:2:3
find the ratio of thier areas
there s a drawing of a circle inside it another 2 smaller
waiting yr active answer
manar
the principle is sound: for similar shapes, the area ratio the square of the linear ratio.atulmangal wrote:IMOmarmar29 wrote:hi all
an archery target has 3 concentric regions. the daimeter of the regions are in the ratio 1:2:3
find the ratio of thier areas
there s a drawing of a circle inside it another 2 smaller
waiting yr active answer
manar
1/4 : 1 : 9/4
let the diameter be x,2x,3x so radius = x/2, x, 3x/2
ratio of area of a circle is proportional to Sq. of radius
hence ratio = 1/4 : 1 : 9/4
I don't think this is the correct answer...if u take some values for diametermarmar29 wrote:thnks for help !
but the answer gvn is 1:3:5 !
how does it come !
@GevaGeva@MasterGMAT wrote:the principle is sound: for similar shapes, the area ratio the square of the linear ratio.atulmangal wrote:IMOmarmar29 wrote:hi all
an archery target has 3 concentric regions. the daimeter of the regions are in the ratio 1:2:3
find the ratio of thier areas
there s a drawing of a circle inside it another 2 smaller
waiting yr active answer
manar
1/4 : 1 : 9/4
let the diameter be x,2x,3x so radius = x/2, x, 3x/2
ratio of area of a circle is proportional to Sq. of radius
hence ratio = 1/4 : 1 : 9/4
So if the diameter ratio is 1:2:3 (which means that the radius ratio is the same 1:2:3, since dividing the ratio by 2 does not change the ratio), the area of the circles with these radii would be 1:4:9.
the error lies in that the question is asking for the ratio of the areas of the concentric regions, not the circle: in other words, the area of each "ring" around the the previous circles.
inner circle has area of 1
middle ring has area of 4-1 =3 (area of middle "ring" is area of middle circle - area of inner circle)
Outer ring has area 9-4=5 (area of outer circle - area of middle circle).
I agree that a GMAT question needs to be indisputable and less ambiguous - meaning that it needs to explicitly state what is the shape of the region it requires the area of - a ring or a circle.atulmangal wrote:@GevaGeva@MasterGMAT wrote:the principle is sound: for similar shapes, the area ratio the square of the linear ratio.atulmangal wrote:IMOmarmar29 wrote:hi all
an archery target has 3 concentric regions. the daimeter of the regions are in the ratio 1:2:3
find the ratio of thier areas
there s a drawing of a circle inside it another 2 smaller
waiting yr active answer
manar
1/4 : 1 : 9/4
let the diameter be x,2x,3x so radius = x/2, x, 3x/2
ratio of area of a circle is proportional to Sq. of radius
hence ratio = 1/4 : 1 : 9/4
So if the diameter ratio is 1:2:3 (which means that the radius ratio is the same 1:2:3, since dividing the ratio by 2 does not change the ratio), the area of the circles with these radii would be 1:4:9.
the error lies in that the question is asking for the ratio of the areas of the concentric regions, not the circle: in other words, the area of each "ring" around the the previous circles.
inner circle has area of 1
middle ring has area of 4-1 =3 (area of middle "ring" is area of middle circle - area of inner circle)
Outer ring has area 9-4=5 (area of outer circle - area of middle circle).
I got your point but please suggest...
can we expect that in GMAT, we get the diagram plus the clarity what exactly the question in asking us to find out??? IMO, In the posted question its not clear what to find out...what do u think???
