What type of number gets a mathematician in trouble the most when trying to use function to model a real world situation? why?

Step-by-step explanation:

Interesting question. Perhaps an inverse relationship.

y = k/x where k is a constant like 10.

The problem begins to become a problem when  x approaches 0 and that happens quite frequently.

I would say as a class of numbers, 0 is the most problematic. 0 was developed about 1100 years after the death of Christ so the concept is pretty subtle. The Romans had no value for 0 as a place holder. 2019 for them was not written with anything that resembled a zero. (MMXIX is how they would write it). That's got to be very awkward when giving parts of an inch in their engineering drawings.

The second group that probably causes some trouble would be the irrationals. pi for one. sqrt(3) for another.  That took a while to develop as well.

susie has 7 apples

(b) 240

step-by-step explanation:

first, we use the pythagorean formula using the given side lengths to find x. then we use x to find the side lengths. then we add the side lengths to find the perimeter.

pythagorean theorem formula:

a^2 + b^2 = c^2

(x - 20)^2 + (x - 40)^2 = x^2

x^2 - 40x + 400 + x^2 - 80x + 1600 = x^2

x^2 -120x + 2000 = 0

(x - 100)(x - 20) = 0

x - 100 = 0 or x - 20 = 0

x = 100 or x = 20

we see that the solution x = 20 must be discarded because it will give a negative side length and a side length of 0. the only valid solution is x = 100.

perimeter = sum of the lengths of the sides

perimeter = x + x - 20 + x - 40

perimeter = 3x - 60

replace x with 100.

perimeter = 3(100) - 60

perimeter = 300 - 60

perimeter = 240