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Teacher III
MATHEMATICS 10
Weeks 3-4 of Quarter 3
Note
Please prepare your scientific
calculator as it will be used in
our online discussion later.
While waiting, think of this!
Below are 5 points on a plane where no
three of which are collinear. How many
triangles can be formed? Type your
answer in the chat box (in-call messages).
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A
B
C D
E
There are 10 triangles formed.
COMBINATION
It is an arrangement of objects in a definite
order.
In permutation, order matters.
It is the selection of objects from a set.
In combination, order does NOT matter.
PERMUTATION
Recall:
PERMUTATION vs. COMBINATION
How many permutations (arrangements)
are there for the letters C, A, and T?
3𝑃3 = 3!
3𝑃3 = 6
{CAT, CTA, ACT, ATC, TCA, TAC}
How many combinations are there for the
letters C, A, and T?
3𝐢3 = 1
CAT, CTA, ACT, ATC, TCA, and TAC are
counted as one.
Combination of 𝑛 objects taken π‘Ÿ
𝒏π‘ͺ𝒓 =
𝒏!
π’βˆ’π’“ !𝒓!
Combination of 𝑛 taken π‘Ÿ at a time where
𝑛 β‰₯ π‘Ÿ β‰₯0
PERMUTATION
If two letters will be formed from the letters
of the word COVID, with or without meaning,
how many arrangements are there?
π‘›π‘ƒπ‘Ÿ =
𝑛!
𝑛 βˆ’ π‘Ÿ !
5𝑃2 =
5!
5 βˆ’ 2 !
5𝑃2 =20
{CO, OC, CV, VC, CI, IC, CD, DC, OV, VO, OI, IO,
OD, DO, VI, IV, VD, DV, ID, DI}
COMBINATION
1. If two letters will be formed from the
letters of the word COVID how many
combinations are there?
π‘›πΆπ‘Ÿ =
𝑛!
𝑛 βˆ’ π‘Ÿ ! π‘Ÿ!
5𝐢2 =
5!
5 βˆ’ 2 ! 2!
5𝐢2 = 10
{CO, OC, CV, VC, CI, IC, CD, DC, OV, VO, OI, IO,
OD, DO, VI, IV, VD, DV, ID, DI}
COMBINATION
2. How many groups composed of 4 persons
each can be formed from 7 students?
π‘›πΆπ‘Ÿ =
𝑛!
𝑛 βˆ’ π‘Ÿ ! π‘Ÿ!
7𝐢4 =
7!
7 βˆ’ 4 ! 4!
7𝐢4 =
7!
3! 4!
7𝐢4 =35
There are 35 groups.
COMBINATION
3. In an essay test, there 5 questions given
where you can choose only 3 of them to
answer. How many ways can you select
questions to answer?
5𝐢3 =
5!
5 βˆ’ 3 ! 3!
5𝐢3 =
5!
2! 3!
5𝐢3 = 10
There are 10 ways.
COMBINATION
4. In a limited party, there are 8 persons
present. If each of them shake hands
exactly with one another, how many
handshakes are there?
8𝐢2 =
8!
8 βˆ’ 2 ! 2!
8𝐢2 =
8!
6! 2!
8𝐢2 = 28
There are 28 handshakes.
Other Problems Involving Combinations
1. In how many ways a group, consisting of
3 boys and 2 girls, can be formed from 6
boys and 4 girls?
6𝐢3 βˆ™ 4𝐢2
20 βˆ™ 6
120 ways
Other Problems Involving Combinations
2. In how many ways a group composed
of 5 members can be formed from 6
boys and 4 girls if there is at least 3
boys in the group?
6𝐢3 βˆ™ 4𝐢2 + 6𝐢4 βˆ™ 4𝐢1 + 6𝐢5 βˆ™ 4𝐢0
120 + 60 + 6
186 ways
Other Problems Involving Combinations
3. From 7 Math books and 6 Science
books, in how many ways can you
select 5 Math and 3 Science books to
buy if all the said books are equally
necessary?
7𝐢5 βˆ™ 6𝐢3
21 βˆ™ 20
420 ways
Other Problems Involving Combinations
4. From 7 Math books and 6 Science
books, in how many ways can you
select 8 books if the number of Math
books to be bought is equal to the
number of Science books?
7𝐢4 βˆ™ 6𝐢4
35 βˆ™ 15
525 ways
Other Problems Involving Combinations
5. From 7 Math books and 6 Science
books, in how many ways can you
select 8 books if there is at least 3
Science books to be selected?
7𝐢5 βˆ™ 6𝐢3 + 7𝐢4 βˆ™ 6𝐢4 + 7C3 βˆ™ 6C5 + 7C2 βˆ™ 6C6
420 + 525 + 210 + 21
1 176 ways
Other Problems Involving Combinations
6. In a singing contest, each contestant
must perform 4 songs with different
genres. If there are 5 choices for rock , 3
choices for R&B, 4 choices for pop, and
2 choices for rap, in how many ways
can the contestant select her piece?
5𝐢1 βˆ™ 3𝐢1 βˆ™ 4𝐢1 βˆ™ 2𝐢1
5 βˆ™ 3 βˆ™ 4 βˆ™ 2
120 ways
Other Problems Involving Combinations
7. If there are 6 distinct points on a plane
with no 3 of which are collinear, how
many quadrilaterals can be possibly
formed?
6𝐢4
15 quadrilaterals
Other Problems Involving Combinations
8. If there are 6 distinct points on a plane
with no 3 of which are collinear, how
many polygons can be possibly formed?
6𝐢3 + 6𝐢4 + 6𝐢5 + 6𝐢6
20+15+6+1
42 polygons
Other Problems Involving Combinations
9. In a pizza parlor, there are 6 different
toppings, where a customer can order
any number of these toppings. If you
dine at the said pizza parlor, with how
many possible toppings can you order
your pizza?
6𝐢1 + 6𝐢2 + 6𝐢3 + 6𝐢4 + 6𝐢5 + 6𝐢6
6 + 15 + 20 + 15 + 6 + 1
63 possible toppings
Applications of Combinations
1. Selecting numbers in a lottery
7-13-26-33-35-42, 35-26-42-7-33-13
2. Selecting fruits for salad
pineapple, grapes, papaya, apple, banana
papaya, banana, apple, pineapple, grapes
3. Choosing members of a committee
Roberto, Romina, Daniela, Marga, Cassie
Marga, Daniela, Roberto, Cassie, Romina
Applications of Combinations
4. Number of handshakes
Rodrigo and Leni, Leni and Rodrigo
5. Selecting problems to solve in a given
list of problems
Answering item 1 followed by 3 and 5
Answering first 3, then 1, and finally 3
Applications of Combinations
6. Using points on a plane to form a
polygon (no three points are collinear)
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