well, from birth to your twentieth birthday that'll just be 20 years, so

Answer:
562 child tickets were sold
217 adult tickets were sold
Step-by-step explanation:
A festival charges $3 for children admission and $5 for adult admission
At the end of the festival they have sold a total number of 779 tickets for $2771
Let x represent the child ticket
Let y represent the adult ticket
x + y= 779..............equation 1
3x + 5y= 2771..........equation 2
From equation 1
x + y = 779
x= 779 -y
Substitute 779-y for x in equation 2
3x + 5y= 2771
3(779-y) + 5y= 2771
2337 - 3y + 5y= 2771
2337 +2y= 2771
2y= 2771 -2337
2y = 434
y = 434/2
y = 217
Substitute 217 for y in equation 1
x + y= 779
x + 217= 779
x = 779-217
x= 562
Hence 562 child tickets were sold and 217 adult tickets were sold
Answer:
(-5, 3)
Step-by-step explanation:
Elimination seems like the best method to use here.
x+y=-2
x-y=-8
---------
2x=-10
Divide everything by two
x=-5
Now plug it back into one of the original equations,
-5+y=-2
Add 5 to everything
y=3
This seems to be referring to a particular construction of the perpendicular bisector of a segment which is not shown. Typically we set our compass needle on one endpoint of the segment and compass pencil on the other and draw the circle, and then swap endpoints and draw the other circle, then the line through the intersections of the circles is the perpendicular bisector.
There aren't any parallel lines involved in the above described construction, so I'll skip the first one.
2. Why do the circles have to be congruent ...
The perpendicular bisector is the set of points equidistant from the two endpoints of the segment. Constructing two circles of the same radius, centered on each endpoint, guarantees that the places they meet will be the same distance from both endpoints. If the radii were different the meets wouldn't be equidistant from the endpoints so wouldn't be on the perpendicular bisector.
3. ... circles of different sizes ...
[We just answered that. Let's do it again.]
Let's say we have a circle centered on each endpoint with different radii. Any point where the two circles meet will then be a different distance from one endpoint of the segment than from the other. Since the perpendicular bisector is the points that are the same distance from each endpoint, the intersection of circles with different radii isn't on it.
4. ... construct the perpendicular bisector ... a different way?
Maybe what I first described is different; there are no parallel lines.