MATHS
1º DE E.S.O
IES FERNANDO III
CENTRO BILINGÜE
MATHS
UNIT 6: RATIOS
UNIT 6: RATIOS
OUTLINE
1 – RATIOS.
2 – WRITING A RATIO IN THE FORM 1:n
OR n:1.
 SOLVING PROBLEMS.
 DIVIDING IN A RATIO.
 DIRECT PROPORTIONS.
3 – DIRECT PROPORTIONS.
4 - VOCABULARY
ASPECTOS LINGÜÍSTICOS



PRESENT SIMPLE
IMPERATIVE
LOS PASADOS
TO BE
THERE WAS
THERE WERE.

VERBOS REGULARES/
IRREGULARES EN
PASADO AFIRMATIVA.
PHONETICS

VOCABULARY











FRACTION
ADDING
SUBTRACTING
MULTIPLYING
DIVIDING
RATIOS
INCREASE
DECREASE
DIRECT PROPORTION
SOLVING PROBLEMS
SCALE DRAWING
LOS PASADOS
REGULARES.
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MATHS
UNIT 6: RATIOS
1.- RATIOS.
A ratio is a way to compare amounts of something. Ratios are similar to fractions: we can simplify them
by using common factors. Always try to divide by the highest common factor.
Example: There are 15 girls and 12 boys in a class. The ratio of girls to boys is 15:12. Both sides of this
ratio are divisible by 3 so:
5 and 4 don’t have common factors. So the simplest form of the ratio is 5:4. This means there are 5 girls in
the class for every 4 boys.
NOTE: You have to be sure that the things you are comparing are measured in the same units.
2 – WRITING A RATIO IN THE FORM 1:n OR n:1.
If we have a ratio 12:15, we can simplify it. We divide both sides by their highest common factor. So
12:15 becomes 4:5. All the numbers are whole numbers in this case. But sometimes we need to write a
ratio in the form 1:n or n:1, where n is a fraction or decimal.
For example, to write 2:5 in the form 1:n we divide both sides by 2.
To write 2:5 in the form n:1, we divide both sides by 5:
Example: Write the ratio 6:9 in
a) the form 1:n
b) the form n:1
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MATHS
UNIT 6: RATIOS
 SOLVING PROBLEMS:
We use ratios to solve many different problems. For example, scale drawings, measures,...
Example: Peter makes a scale drawing of his bedroom. He uses a scale of 1:100. The measures of the
length of the bedroom is 5’9 m. How long is the bedroom on the scale drawing? Give your answer in mm.
The scale of 1:100 means that the real bedroom is 100 times bigger than the scale drawing. 100 m in the
real bedroom is 1 m in the scale drawing, or 100 cm in the real bedroom is 1 cm in the scale drawing. So:
So, in the scale drawing, the measure of the length is 59mm.
Example: This typical example gives you a recipe which can be modified for a different number of
people.
A recipe to make lasagne for 6 people uses 300 grams of minced beef. How much minced beef would be
needed to serve 8 people?
6 people need 300 gr:
Person needs
:
People need
:
Answer: 400gr.

DIVIDING IN A RATIO:
Ratios are also used when dividing amounts . The basic method is:
1) Simplify the ratio, if possible.
2) Add the numbers in the ratio together.
3) Divide the amount by the total number of parts.
4) Multiply the answer by each of the numbers in the ratio.
Example: Mary is 12 years old . Her brother Tom is 9. Their grandfather gives them 140 €, which is to be
divided between them in the ratio of their ages. How much does each of them get?
Answer: The ratio of their ages is 12:9. We can simplify it dividing by 3, and it gives 4:3. So Ann gets 4 parts
and Paul 3. This means that the money has to be divided into 7 parts. (4+3)
So
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MATHS
UNIT 6: RATIOS
3.- DIRECT PROPORTION.
Two quantities are in direct proportion when they increase or decrease in the same ratio. For example, you
could increase something by doubling it, or decrease it by halving it.
Example: Twelve pencils cost 0’72€. Find the cost of 30 pencils.
Answer: To solve this problem we need to know the cost of one pencil. We know that 12 pencils cost 0’72€,
so if we divide 0’72 by to get the cost of one pencil.
So 1 pencil costs 0’06€. Now we need to know the cost of 30 pencils. We multiply 0’06€ by 30:
Problem: Jenny buys 15 pens. It costs her 2’85€. How much would 20 pens cost?
Answer: You divide 2’85 by 15, then multiply the answer by 20.
So
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MATHS
UNIT 6: RATIOS
4.- VOCABULARY
English
Pronunciation
Spanish
Ratio sust
/'reɪʃəʊ/
Proporción
Amounts sust.
/ə'maʊnt/
Cantidad
Common adj.
/'kɑ:mən /
Común
Decrease sust.
/dɪ'kri:s/
Diminuir / disminución(descenso)
Direct proportion adj. and sust.
/daɪ'rekt/
/prə'pɔ:rʃən /
Proporción directa
Dividing up / into verb. and prep.
/də'vaɪd /
Dividir
Double verb. and sust.
/'dʌbəl/
Doblar / doble
Factor sust.
/'fæktər /
Factor
Halving verb.
/hæving/ /hɑ:ving/
Dividiendo por dos, partiendo por la
mitad
In a ratio of two to one
Increase verb. and sust.
En una proporción de dos a uno
Aumentar / aumento
/ɪn'kri:s/
Make a scale drawing
Hacer un dibujo a escala
Measure sust. and verb.
/'meʒər / /'meʒə(r)/
Minced beef adj. and sust.
/mɪnst/ /mi:t/
Medida (nombre)
Medir (verbo)
Carne picada
Recipe sust.
/'resəpi/
Receta
Scale drawing sust.
/skeɪl/
Escala /dibujo
/'drɔ:ɪŋ/
Dibujo a escala
Simplify by common factors
Solve
/sɑ:lv / /sɒlv/
The ratio of girls to boys …
Whole numbers
Resolver
La proporción de chicas respecto a chicos
/həʊl/
/'nʌmbə(r)/
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