Intersections

Change one equation in this pair of simultaneous equations very slightly and there is a big change in the solution. Why?

Negatively Triangular

How many intersections do you expect from four straight lines ? Which three lines enclose a triangle with negative co-ordinates for every point ?

Which Is Cheaper?

When I park my car in Mathstown, there are two car parks to choose from. Which car park should I use?

Which Is Bigger?

Stage: 4 Challenge Level:
Charlie and Alison have filled in their results in the table below.
Can you fill in the rest of the table?
 $n$ $n+10$ $2n+3$ 4 14 11 5 6 7 8 9 10 20 23

What do you notice?