# [ECON 100A] - Final Exam Guide - Everything you need to know! (58 pages long)

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Published on 29 Nov 2016
School
UCSD
Department
Economics
Course
ECON 100A
UCSD
ECON 100A
FINAL EXAM
STUDY GUIDE
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ECON 100A
Erik
elilleth@ucsd.edu
Office: ECON 122
PSET Lab
- Sun 2 – 7
- M Tu Th 5:30 – 9
- W 7 – 9
- ECON 200 for 100A
Problem Set One
Elasticity
1.
a. q = 10 – 2p
E q, p = -2 * p / (10 – 2p)
b. q = p-.5
E q, p = -.5 * p -1.5 * p / p -.5 = -.5
c. q = 1 / ln (p) for p>1
E q, p = -1 / ln (p)2 / p * p / (1 / ln (p)) = -1 / ln (p)
2. E q, p = -2 = % Δ in q / % Δ in p  % Δ in q = -40%
3.
4. q = 150 - .5 p
E q, p = -.5 * p / (150 - .5p)  -1 = -.5 * p / (150 - .5p)  -.5p = -150 + .5p 
p = 150
5. TR = p * q(p)
% Δp = (95 – 100) / 100 = -5%
E q, p = -1.4 ≈ % Δ q / % Δ p  % Δ q = 7%
% Δ TR ≈ % Δ p + % Δ q
≈ -5% + 7%
≈ 2%
6.
7. TR = p * q(p)
d TR/ dp = q(p) + p* q’(p)
= q(p) + q(p) * p / q(p) * q’(p)
= q(p) + q(p) * E q, p
= q(p) * (1+ E q, p)
8.
9.
a. Need f(x) > 0 f’(x) > 0 d E f(x), x / dx < 0
Level curve: set of (x,y) s.t. f(x,y) = c = 1
10. f(x,y) = x+y2
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Solve explicitly for f(x,y)=25
 x+y2 = 25
 y = √(25-x)
dy/dx = - ½ (25-x) – ½ @ (x,y) = (16,3)
dy/dx = - ½ (25 – 16) – ½
= - ½ * 1/ √9
= - 1/6
11. dy/dx|f(x,y) = 25 = - (δf(x,y)/δx) / (δf(x,y)/δy)
= - 1 / 2y
= - 1/6
12. f(x,y) = (x2 + y2)*exy
dy/dx = - (δf(x,y)/δx) / (δf(x,y)/δy)
= - (2x*exy + (x2+y2)*y*exy) / (2y*exy + (x2+y2)*x*exy)
= - (2x + (x2+y2)*y) / (2y + (x2+y2)*x)
13.
f(x,y) = x*y
dy/dx = -y/x
Find ways to increase the denominator
e.g. g(x,y) = (x+1)*y  dy/dx = - y / (x+1)
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## Document Summary

E q, p = -2 * p / (10 2p: q = p-. 5. E q, p = -. 5 * p -1. 5 * p / p -. 5 = -. 5: q = 1 / ln (p) for p>1. 3: q = 150 - . 5 p. E q, p = -. 5 * p / (150 - . 5p) -1 = -. 5 * p / (150 - . 5p) -. 5p = -150 + . 5p p = 150: tr = p * q(p) % p = (95 100) / 100 = -5% E q, p = -1. 4 % q / % p % q = 7% % tr % p + % q. 6: tr = p * q(p) d tr/ dp = q(p) + p* q"(p) = q(p) + q(p) * p / q(p) * q"(p) = q(p) + q(p) * e q, p. 9: need f(x) > 0 f"(x) > 0 d e f(x), x / dx < 0.