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10 Cards in this Set

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  • Back
means per 100, and are ratios in which the second number is always 100
Formula- mixture problems
base x rate = percentage

amount of solution x rate of concentration = amount of pure substance
Formula- interest problems
prt = I

principal x rate x time = Interest
A chemist needs to mix 20L of a 40% acid solution with some 70% acid solution to obtain a mixture that is 50% acid. How many liters of the 70% acid solution should be used?
.70x = 70% acid sol.
.40 (20L) = 40% acid sol.
.50(x + 20) = 50% acid sol.

.70x + .40(20) = .50(x+20)

Answer: Chemist will need 10L of 70% sol.
Elizabeth Suco recieves an inheritance. She plans to invest part of it at 6% and $2000 more than this amount at 7%. To earn $790 per year in interest, how much should she invest at each rate.
I =prt

I = $790
.06x = amt invested @ 6%
.07(x = 2000) = amt invested @ 7%

.06x = .07(x +2000) = $790

answer: 5k invested @ 6%
7k invested @ 7%
Problems with different denominations are similar to what type of problems?
mixture & interest problems
Formula for money denomination problems?
number x value of one item = total value
A bank teller has 25 more $5 bills than $10 bills. The total value is $200. How many of each denomination of bill does she have?
x = # of $10 billa
x + 25 = # of $5 bills
$200 = total value of money

10x + 5(x + 25) = 200

Answer: 5 tens
30 fives (25 + 5)
two cars leave Baton Rouge, Louisiana at the same time and travel east on I-10. One travels at constant speed of 55 mph, and the other travels at a constant speed of 63 mph. In how many hours will the distance between them be 24 miles?
d = rt

d = 24mi
55t = slower car
63t = faster car

63t - 55t = 24

answer: 3 hours
Two planes leave memphis at the same time. One heads south to New Orleans. The other plane heads north to Chicago. The Chicago plane flies 50 mph faster than the New Orleans plane. In 1/2 hour the planes are 275 miles apart. what is their speeds
d =rt

Solving for rate:

r = slower New Orleans Plane
r + 50 = faster chicago plane
275 = distance apart after 1/2 hour


New Orleans Plane= 250mph
Chicago Plane= 300mph (250 + 50)