# Ratios and Proportions

This week’s topic has been Ratios and Proportions. Let’s go through that blue SAT book everyone has, http://amzn.to/1wADKLS, or http://amzn.to/1wtPZuD, and this ACT book for problems about ratios that can be solved using my TI-84 Plus programs RATIO and PROPORTN.  (See these posts for examples: 10/27, 10/28, 10/29, 10/30) Sorry, I won’t post the actual problems here.  […]

# Ratios

Q: Last month, the ratio of sunny days to rainy days was 3:2.  How many rainy days  were there last month, if the month had 30 days?  (Assume all days were either sunny or rainy.)   . . . . Answer: 12 Solution by hand: Number of sunny days = 3x Number of rainy days = 2x 3x + 2x […]

# Ratios

Q:  The ratio of blue cars to non-blue cars in the parking lot is 2:7.  If there are 1260 cars in the parking lot, how many are blue? . . . .   Answer: 280 Solution by hand: Number of blue cars = 2x Number of non-blue cars = 7x 2x + 7x = 1260 […]

# SAT / Algebra 1: Ratios

Q:  In my box of cereal, the ratio of flakes to raisins is 9:2. If there are a total of 220 flakes and raisins in the box, how many of these are flakes?   Answer:  180 Explanation:  Solve the equation: 9x + 2x = 220 to get x = 20.  ‘Flakes’ are the 9x part […]

# Proportions

Q:  x is inversely proportional to w.  If x = 6 when w = 8, what is x when w = 12? . . . .   Answer: 4 Solution by hand: For inverse proportions, (x1)(w1) = (x2)(w2) (6)(8) = (x)(12) 48 = 12x x=4 Solution using my TI-84 Plus Program PROPORTN: Run PROPORTN.  How? x1 […]

# Proportions

Let’s change yesterday’s question around a bit: Q:  Wandering around blindly in a parking lot (don’t try it, please), the probability that the first car you bump into is blue is 2/5.  If there are 500 blue cars, how many cars are in the parking lot? . . . .   Answer: 1250 Solution by hand: Set up the […]

# Algebra 2 – Sequences

Q: What is the tenth term of the sequence: 4, 12, 36, 108, …? Answer:  78732 Explanation:  It’s a geometric sequence because each term is multiplied by 3 to get the next term. The common ratio (r) is 3. You *could* just keep multiplying by 3 until you get to the tenth term. It’s not […]