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Park Forest Math Team
Self-study Packet
Meet #2 try-outs are November 21
Meet #2 is December 5 at Mt. Nittany from 4:30-6:30
Problem Categories for this Meet:
1.
2.
3.
4.
5.
Mystery: Problem solving
Geometry: Area and perimeter of polygons
Number Theory: Divisibility GCF, LCM, prime factorization
Arithmetic: Fractions, terminating and repeating decimals, percents
Algebra: Word problems with 1 unknown; working with formulas; reasoning
in number sentences
Meet #2 – Algebra
Ideas you should know:
! Common Fraction:
! Money Answers:
23¢
“What is One-Quarter of a dollar, minus two cents?”
$0.23
! Square Root of a Product:
$.23
Not 0.23¢
Not 23
“What is the square root of 14x21 x 6?”
! Slow hard way – “Multiply it out first”:
14x21=294,
294x6=1764,
“Um, Are we allowed to
use calculators? How are we supposed to do this?”
" Faster way – “Factor it first”:
From question:
14
21
6
Factor:
2x7
3x7
2x3
Regroup factors:
2x2
3x3
7x7
=3
=7
Now do !
Answer:
2x3x7=42
! “Five consecutive multiples of 5 have a sum of 250 …” problems:
40
45
50
55
60
Average=50
If 5 numbers add to 250, the average is 50. That’s also the middle number,
so the five numbers are 40,45,50,55,60. Often the problem will ask for the
2nd number times the 4th number (45 x 55 here).
Meet #2, Algebra
! “Four times the sum of a number and one is two more than
seven times an amount one less than the number.
Find the number.”
So confusing!
Make N be the number you don’t know, then translate the
words to Algebra:
Four times the sum of a number and one is two more than
4
x
(
N
+
1)
-2
=
Seven times an amount one less than the number
7
Or:
x
(
N
-
1)
4 (N+1) – 2 = 7 (N-1)
Find the number.
Solve for N.
First, distribute, then combine like terms:
4N + 4 – 2 = 7N – 7
4–2+7
9
(Add 7 – 4N to each side)
= 7N – 4N
= 3N
3=N
Then check this answer in the original problem!
“Four times (3+1) is two more than 7(3-1)”
Meet #2, Algebra
Yes, 14=14
!
Relatively Prime (review): Having no common factors besides 1. 100 and
99 are relatively prime, since the only prime factors of 100 are 2 and 5, and
99 has 3 and 11.
Are 6 and 10 relatively prime?
No, both share 2 as a factor.
Are 27 and 111 relatively prime?
No, both share 3 as a factor.
Are 35 and 66 relatively prime?
Yes, 35 is 5x7, 66 is 2x3x11.
How many natural numbers less than 10 are relatively prime to 10, counting
1 as relatively prime to everything?
Answer: 4: 1,3,7,9
How many whole numbers less than 17 are relatively prime to 17?
P3
! Subscripts like P3 : pronounced “P sub three”
If P = {2, 3, 5, 7, 11, 13, 17, 19, 23, …} then
P1 = 2
P2 = 3
P3 = 5
If Pn=19, what is n?
P3 just means the 3rd P in a list. For example, if M is the set of how much
money Anna, Bridget, and Caroline have, MAnna (pronounced M sub Anna) is
how much money just Anna has.
If T is the set of multiples of 3: T = {3, 6, 9, 12, …} then T2=6, and Tn=3n
Answer to Pn=19: n=8.
! Time for some real problems from previous meets.
Meet #2, Algebra
Category 5
Algebra
Meet #2, November, 2002
1. A plumber charged a flat fee of $50 to come to the house, plus an hourly rate
for the time he spends working at the house. If the plumber stayed for three and a
half hours and charged a total of $274, what is his hourly rate? Express your
answer in dollars.
2. Five less than three times the sum of a number and eleven is equal to seventythree minus four times the sum of the number and six. What is the number?
2
3. The formula for the surface area of a torus (a donut) is S = 2πr ⋅ 2πR= 4π rR,
where r is the radius of a cross section of the ring and R is the radius from the
center of the hole to the center of the ring. (See diagram below.) Imagine a perfect
chocolate frosted donut with r = 0.5 inches and R = 1.5 inches. If exactly half of
this donut is covered with chocolate frosting, how many square inches of the
surface of the donut is covered with frosting? Use 3.14 for ! and round your
answer to the nearest tenth.
Answers
1. _______________
2. _______________
3. _______________
Solutions to Category 5
Algebra
Meet #2, November, 2002
Answers
1. 64
2. 3
3. 14.8
1. From the details given, we can write the following
equation: 3.5x + 50 = 274, where x is the hourly rate.
Subtracting 50 from both sides of the equation, we get:
3.5x = 224. Dividing both sides of the equation by 3.5,
we get x = 64. The plumber’s hourly rate is $64.
2. The verbal sentence translates to the following
equation:
3(x +11)− 5 = 73− 4(x + 6)
. Distributing the
multiplication over each addition, we get
3x + 33− 5 = 73− 4x − 24 and then 3x + 28= 49− 4x .
Adding 4x and subtracting 28 from each side of the
equation, this becomes: 7x = 21. x = 3 is the solution to
this equation, so the number must be 3.
3. Substituting 0.5 for r and 1.5 for R in the formula
S = 4π 2rR, we get S = 4⋅ π 2 ⋅ 0.5⋅1.5.
Since 4⋅ 0.5⋅ 1.5 = 2⋅ 1.5 = 3, the surface of the whole
2
donut is S = 3⋅ π and the surface of half the donut
1
3
S= ⋅π 2
2
would be 2
. Using 3.14 for !, we get:
3
3
⋅ 3.142 = ⋅ 9.8596= 3⋅ 4.9298= 14.7894
2
2
.
Rounding this to the nearest tenth, we can say that about
14.8 square inches of the surface of the donut is covered
in chocolate frosting.
Category 5
Algebra
Meet #2, November 2004
1. Five consecutive multiples of 11 have a sum of 1155. What is the product of
the second and the fourth of these five numbers?
2. At a school play, tickets for students cost $3 and tickets for adults cost $5. If
620 tickets were sold and a total of $2660 was made, how many adults bought
tickets for the play?
abc
can be used to calculate the radius of a circle that
4 ⋅ ATriangle
is circumscribed around a triangle, where a, b, and c are the side lengths of the
triangle and ATriangle is the area of the triangle. The formula
3. The formula R =
ATriangle = s (s − a )(s − b)(s − c) can be used to calculate the area of a triangle,
where a, b, and c are again the side lengths of the triangle and s is the
semiperimeter (half the perimeter). Find the radius of the circle that circumscribes
a triangle with side lengths 13, 14, and 15 units. Express your
result in lowest terms as a common fraction, not a mixed number.
b
a
Answers
1. _______________
2. _______________
3. _______________
R
www.Imlem.org
c
Solutions to Category 5 Average team got 9.17 points, or 0.8 questions correct
Algebra
Meet #2, November 2004
Answers
1. 53240
2. 400
3.
65
8
1. If five consecutive multiples of 11 have a sum of 1155,
then their average is 1155 ÷ 5 = 231, which is also the
middle number. The five multiples of 11 are: 209, 220,
231, 242, and 253. The product of the second and forth of
these is 220 × 242 = 53240.
2. If the same number of tickets had been sold to students
and adults, the average ticket price would have been $4 and
the total ticket sales would have been $4 × 620 = $2480.
Since the total ticket sales was $2660, we know that there
were more adults than students. The difference $2660 –
$2480 = $180, tells us that there were 180 more adult
tickets than student tickets. Subtracting these excess adults
tickets from the 620 tickets, we get 440 tickets that were
sold equally to adults and students. Thus there were 220
student tickets sold and 220 + 180 = 400 adult tickets.
3. First we need to plug the values 13, 14, and 15 into the
equation for the area of the triangle. The semiperimeter is s
= (13 + 14 + 15) ÷ 2 = 42 ÷ 2 = 21.
ATriangle = 21(21−13)(21−14 )(21−15)
= 21⋅ 8 ⋅ 7 ⋅ 6
= 2 4 ⋅ 32 ⋅ 7 2
= 22 ⋅ 3 ⋅ 7
= 84
Now we can use the first formula to find the radius of the
circumscribed circle.
13⋅14 ⋅15 13 ⋅ 5 65
R=
=
= .
4 ⋅ 84
4⋅2
8
www.Imlem.org
Category 5
Algebra
Meet #2, December 2006
1. Use the five equations below to find the value of A.
A 2 = 92 − B
B=C+5
D
4
D = 3E 4
2C =
E 5 = 32
2. The formula for the area of an equilateral triangle with side length s is
s2 3
A=
. A regular hexagon can be subdivided into six equilateral triangles as
4
shown in the figure below. If the area of a regular hexagon is 600 3 square
centimeters, how many centimeters are in the side length of the hexagon?
3. The sum of three consecutive multiples of 29 is equal to the sum of four
consecutive multiples of 9. If the smallest of the four multiples of 9 is 117, what
is the value of the greatest of the three multiples of 29?
Answers
1. _______________
2. _______________
3. _______________
www.imlem.org
Solutions to Category 5
Algebra
Meet #2, December 2006
Answers
1. 9 (or -9)
2. 20
3. 203
1. Starting with the last equation and working our way back up,
we find that E = 2, D = 48, C = 6, B = 11, and A = 9.
-9 is also an acceptable answer, as (-9)2=81.
2. First we will equate the area we are given with six times the
formula for the area of an equilateral triangle. Then we will
solve for the side length s.
!s2 3$
600 3 = 6#
&
" 4 %
Dividing both sides of the equation by 6 and by 3 , we get
s2
100 = . Next, we multiply both sides of the equation by 4,
4
which gives us 400 = s 2 . Since 202 is 400, the side length of
the hexagon must be 20 centimeters.
3. The four consecutive multiples of 9 must be 117, 126, 135,
and 144. Their sum is 522. Dividing 522 by 29, we get 18.
Students with
correct answer in a Since 5 + 6 + 7 = 18, we can figure out that the three
cluster of 6 schools: consecutive multiples of 29 must be 5 × 29 = 145, 6 × 29 =
174, and 7 × 29 = 203, which is the greatest.
1. 34/36
2. 23/36
3. 25/36
.
www.imlem.org
Category 5
Algebra
Meet #2, December 2008
1.
The sum of 5 consecutive odd numbers is 105. What is the largest of the 5
numbers?
2.
Shandra and Terri are sisters who were both given the same amount of
money by their mother. Shandra was able to triple her money doing chores,
while Terri spent 6 of her dollars. Shandra now has 4 times as much money
as Terri. How many dollars did Terri’s mother give her?
3.
The sum of the first n natural numbers is known as the nth triangular number.
"$"%&'
The formula for the nth triangular number is !" #
. The sum of the
(
first n cubic numbers is equal to the nth triangular number squared. If the
sum of the first n cubes is 6084, what is the value of n?
Answers
1. _______________
2. _______________
3. _______________
Solutions to Category 5
Algebra
Meet #2, December 2008
1. By calling the middle of the five odd numbers !, we can
use the equation below to find the middle number
"! # $% & "! # '% & ! & "! & '% & "! & $% (105
)! ( *+) , ! ( '*
If the middle number is 21, then the five numbers are 17, 19,
21, 23, 25.
Answers
1.
25
2.
24
3.
12
2. Calling the amount of money Terri and Shandra started with
-, we can use the equation .- ( $"- # /% , .- ( $- # '$ ,
- ( '$.
3. The sum of the first n cubes is equal to "01 %2 , so the first thing we need to
figure out is the square root of 6084. We can estimate this by noticing that
3+2 ( /$++ so we know the square root is less than 80. Since the number ends in
4 its square root must end in 2 or 8. So the square root of 6084 is either 72 or 78
(since we know it is an integer). 722 = 5184 and 782 = 6084. We now know that
1"156%
01 ( 43 (
, *)/ ( 7"7 & *% , *' 8 *. ( 7"7 & *% , *' ( 7
2
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