Exercise
3.3
1. Fill in the boxes.
(i) 3 : 5 : : ___ : 20
(ii) : 24 :: 3 : 8
(iii) 5 : 10 : 8 :: 15:
Answer: 4, 12
(iv) 12 : =
: 4 = 8 : 16
2. Say True
or False.
(i) 2 : 7 :: 14 : 4
(ii) 7 Persons is to 49 Persons as 11 kg is to 88 kg
(iii) 10 books is to 15 books as 3 books is to 15
books
3. Using the numbers 3, 9, 4, 12 write two ratios
that are in proportion.
Solution:
Using numbers = 3, 9, 4, 12
Ratios in proportion
(i) 3 : 9 : : 4 : 12
(ii) 9:3:: 12: 4
4. Find whether 12, 24, 18, 36 in that order can
be expressed as two ratios that are in proportion.
Using numbers = 12, 24, 18, 36
Two ratios = (i) 12 : 24
(ii) 18:36
Proportion :− 12 : 24 :: 18 : 36
5. Write the mean and extreme terms in the following
ratios and check whether they are in proportion.
(i) 78 litres is to 130 litre and 12 bottles is
to 20 bottles
(ii) 400 gm is to 50 gm and 25 rupees is to 625
rupees
Solution:
(i) 78: 130:: 12:20
extreme = 78 × 20 = 1560
mean = 130 × 12 = 1560
extreme = mean
Ratios are in proportion
(ii) 400 : 50 : : 25 : 625
extreme = 400 × 625 = 250000
mean = 50 × 25 = 1250
extreme ≠ mean
Ratios are not in proportion
6. The America’s famous Golden Gate bridge is 6480
ft long with 756 ft tall towers. A model of this bridge exhibited in a fair is 60
ft long with 7 ft tall towers. Is the model in proportion to the original bridge?
Solution:
Bridge Ratio = 6480:756
Model Ratio = 60 : 7
proportion = 6480 : 756 :: 60 : 7
extreme = 6480 × 7 = 45360
mean = 756 × 60 = 45360
extreme = mean
The model is in proportion.
Objective
Type Questions
7. Which of the following ratios are in proportion?
(a) 3 : 5 , 6 : 11
(b) 2 : 3, 9 : 6
(c) 2 : 5, 10 : 25
(d) 3 : 1, 1 : 3
Answer: (c) 2 : 5, 10 : 25
8.
If the ratios formed using the numbers 2, 5, x, 20 in the same
order are in proportion, then ‘x’ is
(a)
50
(b)
4
(c)
10
(d)
8
Answer: (d) 8
9.
If 7 : 5 is in proportion to x : 25, then ‘x’ is
(a)
27
(b)
49
(c)
35
(d)
14
Answer: (c) 35
Answers:
Exercise 3.3
1) (i) 12 (ii) 9 (iii) 4; 12 (iv) 24; 2
2) (i) False (ii) False (iii) False
3) (i) 3 : 9 : :4:12 (ii) 9 : 3 : :12:4
4) Yes
5) (i) Yes (ii) No
6) Yes
7) (c) 2 : 5 , 10 : 25
8) (d) 8
9) (c) 35
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