gmat prep 2

[girishbtg]

[sanju09]

We have AB = OC = OB = r, the radius of circle in question. What is ∠BAO?

≡ ∠BAO = ∠BOA = let x =?

∴ ∠CBO = ∠BCO = 2 x.

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, we have a linear in x, sufficient

[2] If ∠BCO = 2 x = 40º, then x = 20º, sufficient


[spoiler]D[/spoiler]

[girishbtg]

We have AB = OC = OB = r, the radius of circle in question. What is ∠BAO?

≡ ∠BAO = ∠BOA = let x =?

∴ ∠CBO = ∠BCO = 2 x.

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, we have a linear in x, sufficient

[2] If ∠BCO = 2 x = 40º, then x = 20º, sufficient


[spoiler]D[/spoiler]

Thanks for Responding...

but still am not able to find out that how A ( i.e. eq 1 ) is sufficient in itself... Plz elaborate

Thanks!

[sanju09]

We have AB = OC = OB = r, the radius of circle in question. What is ∠BAO?

≡ ∠BAO = ∠BOA = let x =?

∴ ∠CBO = ∠BCO = 2 x.

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, ∠COB + ∠BOA = 120º

Or, we have a linear in x, sufficient

[2] If ∠BCO = 2 x = 40º, then x = 20º, sufficient


[spoiler]D[/spoiler]

Thanks for Responding...

but still am not able to find out that how A ( i.e. eq 1 ) is sufficient in itself... Plz elaborate

Thanks!

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, 180º - 4 x + x = 120º

Or, x = 20º. Hence, sufficient

[girishbtg]

We have AB = OC = OB = r, the radius of circle in question. What is ∠BAO?

≡ ∠BAO = ∠BOA = let x =?

∴ ∠CBO = ∠BCO = 2 x.

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, ∠COB + ∠BOA = 120º

Or, we have a linear in x, sufficient

[2] If ∠BCO = 2 x = 40º, then x = 20º, sufficient


[spoiler]D[/spoiler]

Thanks for Responding...

but still am not able to find out that how A ( i.e. eq 1 ) is sufficient in itself... Plz elaborate

Thanks!

[1] If ∠COD = 60º, then ∠COA = 120º

Or, ∠COB + ∠BOA = 120º

Or, 180º - 4 x + x = 120º

Or, x = 20º. Hence, sufficient

Great...!

Thanks!

[GMATGuruNY]

When you want to see how the angles in a figure affect each other, plug in twice. The attached .pdf shows two sets of angle measurements that satisfy the requirements of the figure. In each case, we can see that COD:BAO = 3:1 and that BCO:BAO = 2:1.

Statement 1:
If COD = 60, then 60:BAO = 3:1, and BAO = 20. Sufficient.

Statement 2:
If BCO = 40, then 40:BAO = 2:1, and BAO = 20. Sufficient.

The correct answer is D.