I am confused, Why does y appear twice in the figure, and what does it mean (B is an exterior angle y°)?

NOTE: The (poorly drawn) diagram tells us that ∠y = ∠ABC


Given: ABC is a right triangle

This means that EITHER x = 90° and y = 70° OR y = 90° and x = 70°
This means we can already ELIMINATE answer choices A, B and C


Let's see what happens if x = 90° and y = 70°
Since angles on a line must add to 180°, we can see that that ∠BDC = 110°
This causes a big problem
If we focus on triangle BDC (below)...

... we can see that two of the angles (90° and 110°) already add to 200°, which breaks the rule that says angles in a triangle always add to 180°
So it can't be the case that x = 90° and y = 70°
ELIMINATE answer choice D

By the process of elimination, the correct answer is E

Cheers,
Brent

From angle D

y + d = 180


d = 180 - y

Split B into a and b and let b be part of DBC

From triangle DBC

b + 180 - y + x = 180

b = y - x

We can clearly see that if ABC is a right angled triangle and b cant be negative that means y > x

y is definitely 90

Answer E

Adewale Fasipe, quant instructor from Lagos Nigeria.