### 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. Can you help me to decide which one to use?

# Which Is Bigger?

##### Age 14 to 16 Challenge Level:

You may wish to explore the problem Which Is Cheaper? before working on this task.

Which is bigger, $n+10$, or $2n+3$?
How did you decide?

Here's how I decided:

"I wonder what happens when $n=4$."
"$4+10=14$ but $2 \times 4 + 3$ is only $11$."
"So it looks like $n+10$ is bigger."

But then my friend said:

"I wonder what happens when $n=10$."
"$10+10=20$ but $2 \times 10 +3$ is $23$."
"So it looks like $2n+3$ is bigger."

Can you explain why we have come to different conclusions?
Is there a diagram you could draw that would help?

For the following pairs of expressions, can you work out when each expression is bigger?

$2n+7$ and $4n+11$
$2(3n+4)$ and $3(2n+4)$
$2(3n+3)$ and $3(2n+2)$

Here are some challenges to try:
• Find two expressions so that one is bigger whenever $n< 5$ and the other is bigger whenever $n> 5$.
• Find three expressions so that the first is biggest whenever $n< 0$, the second is biggest whenever $n$ is between 0 and 4, and the third is biggest whenever $n> 4$.
• Find three expressions so that the first is biggest whenever $n< 3$, the second is biggest when $n> 3$, and the third is never the biggest.
• Find three expressions so that one of them is the biggest regardless of the value of $n.$