Page 85 - Maths Skills - 7

Comparing Quantities 83

CONTINUED PROPORTION
When the second and the third term of a proportion are the same number, we call it a continued proportion, i.e., if
a : b : : b : c, then a, b and c are in continued proportion.
For example; 2 : 6 : : 6 : 18 ; 7 : 28 : : 28 : 112 ; 1 : 5 : : 5 : 25 are in continued proportion.

Let’s Attempt

Example 1: Sohail purchased 12 pens for ` 96. If he wants to buy 20 pens for the same price, how much does
he have to pay?
Solution: Let the cost of 20 pens be ` x.

Here 12 : 20 : : 96 : x
Product of the extremes = 12x
Product of the means = 20 × 96
⇒ 12x = 20 × 96

or x = 20 × 96
12

x = ` 160

Example 2: Tanya has 14 chocolates. She wants to divide the chocolates in the ratio of 3 : 4 among her two
brothers. Find the share of each brother.

Solution: Given ratio is 3 : 4 and 3 + 4 = 7
Total chocolates Tanya has = 14
3
One brother will get × 14 = 6 chocolates
7
4
and other will get × 14 = 8 chocolates.
7
(You may also find other brother’s share by subtracting, i.e., 14 – 6 = 8)

Example 3: Find the ratio of 8 hr to 1 day.
Solution: As hours and day are the units of time, but not equal. So, we convert 1 day in hours, i.e.,
1 day = 24 hr
So, the ratio is 8 : 24

⇒ 8 = 1
24 3
⇒ 1 : 3 Alternative Approach

3
Example 4: Which ratio is greater: 3 : 5 or 5 : 8? 3 : 5 = , 5 : 8 = 5
3 5 8
Solution: 3 : 5 = = 0.6 LCM of 5 and 8 = 40
5
5 ⇒ 3 × 8 = 24
5 : 8 = = 0.625 5 × 8 40
8
⇒ 5 : 8 is greater. and 5 × 5 = 25
8 × 5 40
25 > 24
⇒ 5 : 8 > 3 : 5