Fresh 2 Flashcards
(79 cards)
“There is no integer n such that x is divisible by n and
1 < n < x.”
What does this statement mean?
x is prime.
If there is no integer smaller than x and greater than 1 that will deliver an integer when x is devided by it, then x has only two factors: 1 and itself. x = prime
Solve using Test Cases strategy
If p, q and r are integers, is pq + r even?
(1) p + r is even
(2) q + r is odd
E
You score 80 in your mid-term exam and 100 on your final exam. Only these two exams make up your final grade of 92. How heavily did your teacher weight the final exam?
60%
Let the weighting of the 100 grade be x.
80(1 - x) + 100x = 92
20x = 12
x = 3/5 = 60%
Write the expression of 3 less than X.
X - 3
x > y
Is 1/x > 1/y?
No.
When numbers are reciprocals, the inequality sign changes. For example x = 4 and y = 3
4 > 3 and 1/4 < 1/3
Greg, Marcia, Peter, Jan, Bobby and Cindy go to a movie and sit next to each other in 6 adjacent seats in the front row of the theater. If Marcia and Jan will not sit next to each other, in how many different arrangements can the six people seat?
Arrangements with constraints
First, we calculate the total possibilities of arrangements:
6! = 720
Now we take the constraints. It will be easier to calculate the number of cases in which Jan and Marcia would sit together and then subtract. Here woulc be usefull to use the glue method (like Marcia and Jan are glued as one person). So, the posibilities would equal 5! = 120
Now, 120 * 2 = 240 (since they can sit as J - M or M - J)
720 - 240 = 480 possible combinations
If n is a positive integer, how many of the ten digits from 0 through 9 could be the units digits of n^3 ?
A. Three
B. Four
C. Six
D. Nine
E. Ten
E.
Test cases:
Can it be 0? Yes, 10^3=1,000.
Can it be 1? Yes, 1^3=1.
Can it be 2? Yes, 8^3=512.
Can it be 3? Yes, 7^3=343.
Can it be 4? Yes, 4^3=64.
Can it be 5? Yes, 5^3=125.
Can it be 6? Yes, 6^3=…6.
Can it be 7? Yes, 3^3=27.
Can it be 8? Yes, 2^3=8.
Can it be 9? Yes, 9^3=…9.
Three grades of milk are 1 percent, 2 percent and 3 percent fat by volume. If x gallons of the 1 percent grade, y gallons of the 2 percent grade, and z gallons of the 3 percent grade are mixed to give x+y+z gallons of a 1.5 percent grade, what is x in terms of y and z?
We know that 1%x + 2%y + 3%z = 1.5%(x + y + z)
Thus,
x + 2y + 3z = 1.5x + 1.5y + 1.5z
0.5x = 0.5y + 1.5z (multiply by 2)
x = y + 3z
If x and k are integers and (12x)[4(2x+1)] = (2k)(32), what is the value of k?
k = 14
10x = (4y)(5z)
If x, y, and z are integers, is x even?
Yes.
10x = (4y)(5z)
(2x)(5x) = (22y)(5z)
Thus, x = 2y and z = x.
2y is even (any number multiplied by 2 is even), x must be even too.
If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?
(1) The range of the n integers is 14
(2) The greatest of the n integers is 17
D.
What is the difference of the meaning between:
- “Point x lies on the circle.”
- “Point x lies in the circle.”
- On the circle means that x lies on the circles border, on its circumference.
- In the cirle means that point x lies inside the circle, not on its circumference.
Renee has a bag of 6 candies, 4 of which are sweet and 2 of which are sour. Jack picks two candies simultaneously and at random. What is the chance that exactly 1 of the candies he has picked is sour?
Probability trees
- First candy will be wither sweet or sour. 2/6 chance it will be sour and 4/6 chance it will be sweet.
- If the first candy we pick is sour, than the second candy has 1/5 chance to be sour and 4/5 chance to be sweer. Thus, the probability to get only one sour candy when the first candy is sour = 2/6 * 4/5 = 4/15
- If the first candy we pick is sweet, than the second candy has 2/5 chance to be sour and 3/5 to be sweet. Thus, the probability to get only one sour candy when the first candy is sweet = 4/6 * 2/5 = 4/15
It results that the probability of getting only one sour candy = 4/15 + 4/15 = 8/15
What is the GCF and LCM of 18 and 32?
First we have to factor out each term.
18 = 3 * 3 * 2
32 = 2 * 2 * 2 * 2 * 2
GCF = product of the smallest number of factors, thus = 2
LCM = the product of the greatest number of factors, thus = 25 * 32 = 32 * 9 = 288
GCF = 2
LCM = 288
Check Number Properties p. 84
Alicia lives in a town whose streets are on a grid system, with all streets running east-west or north-south without breaks. Her school, located on a corner, lies three blocks south and three blocks east of her home, also located on a corner. If Alicia s equally likely to choose any possible path from home to school, and if she only walks south or east, how many possible routes can she take to school?
Disguised combinatorics.
Alicia goes 6 blocks and she has to make 6 choices whether to go south or east, but she has only 3 choices south and 3 choices east, she does not go further.
Thus,
6! / 3!3! = 20
If n and k are positive integers, is n divisible by 6?
(1) n = k(k + 1)(k - 1)
(2) k – 1 is a multiple of 3
A.
(1) We know that n is the product of 3 consecutive integers. It is sufficient. Try test cases.
(2) It tells us nothing about n
At a certain pizzeria, 1/8 of the pizzas sold in one week were mushroom and 1/3 of the remaining pizzas sold were pepperoni. If n of the pizzas sold were pepperoni, how many were mushroom (in terms of n) ?
Remaining pizzas = 1 - 1/8 = 7/8
n = (1/3)(7/8)total
n = (7/24)total
total = (24/7)n
nr of mushroom pizzas = (1/8)(24/7)n = (3/7)n
Danny scored on the first exam 75 and on the second 92. If first exam counts to 40% of final score and second exam counts to 60% of the final score, what is Dannys final score?
75 * 0.4 + 92 * 0.6 = 85
The length of a rectangular floor is twice its width. The floor is partially covered by a rectangular carpet whose length is the same as the lenfth of the floor and whose width is two feet less than the width of the floor. If the area of the carpet is 160 sq. feet, what is the length, in feet, of the floor?
A. 8
B. 16
C. 20
D. 24
E. 32
C.
160 = (w - 2)(2w)
w = 10
10 * 2 = 20
Expressions
Salesperson A’s compensation for any week is $360 plus 6 percent of the portion of A’s total sales above $1,000 for that week. Salesperson B’s compensation for any week is 8 percent of B’s total sales for that week. For what amount of total weekly sales would both salepeople earn the same compensation?
15.000$
360 + 0.06(x - 1000) = 0.08x
0.02x = 300
x = 15000
A total of 30 percent of the geese included in a certain migration study were male. If
some of the geese migrated during the study and 20 percent of the migrating geese were
male, what was the ratio of the migration rate for the male geese to the migration rate for
the female geese?
[Migration rate for geese of a certain sex = (number of geese of that sex migrating) /
(total number of geese of that sex)]
A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7
B.
Let there be g geese, of which 0.3g are male and 0.7g are female
Lets say m geese migrated, 0.2m are male and 0.8m are female
Migration Rate Male = 0.2m / 0.3g = (2/3)*(m/g)
Migration Rate Female = 0.8m / 0.7g = (8/7)*(m/g)
Ratio of migration rates = (2/3) / (8/7) = 7/12
In a mayoral election, Candidate X received 1/3 more votes than candidate Y, and Candidate Y received 1/4 fewer votes than Z. If Z received 24,000 votes how many votes did candidate X received?
X = 4/3Y
Y = 3/4Z
X = 4/3 * 3/4Z
X = Z
Thus, X = 24.000
For every integer k from 1 to 10, inclusive the “k”th term of a certain sequence is given by (−1)(k+1) * (1/2k) if T is the sum of the first 10 terms in the sequence, then T is:
A. greater than 2
B. between 1 and 2
C. between 1/2 and 1
D. between 1/4 and 1/2
E. less than 1/4
D.
Try to input the first terms to see the tendency. It is very slowly growing from 1/4. Trying 3 - 4 terms is enough to understand that the sum wont get above 1/2 but will be bigger than 1/4.
What is the probability that the sum of two number cubes will yield a 10 or lower?
Two number cubes = 36 total posibilities.
It is easier to find the posibilities that the cubes will yield a 11 or higher and to subtract the result from 1.
To have a 11 we will need: 6 + 5 or 5 + 6 2 cases.
To have a 12 we will need: 6 + 6 1 case.
Thus, 1 - 3/36 = 33/36 = 11/12