Hence, 4 : 5 is greater than 3 : 4
The idea may be explained through exercises. To get mastery of the idea, the child
may be asked to work out a few problems in ratio on his own.
- Proportion
Proportion is an equality of two ratios. In any proportion the product of two extremes
will always be equal to the product of the two means.
Eg. : The cost of 4 notebooks is 24 and the cost of 7 notebooks is Rs. 42. What is the
proportion?
The ratio of two quantities = 4 : 7
The ratio of their costs = 24 : 42
Therefore, the proportion is 4 : 7 = 24 : 42
Note : In the above proportion, the first and the fourth terms (4 and 42) are called
the extreme terms or extremes. The second and the third terms (7 and 24) are
called the middle terms or means.
The idea may be explained to the child through demonstration by using beads. Emphasis
must also be laid in enabling the child to work out a few sums on his own.
- Direct variation
If two quantities vary always in the same ratio then they are said to be in direct
variation. In other words, if two quantities vary inversely such that one of them
increases as the other increases, they are said to be indirect variation.
Eg. 1 :
A pen costs Rs.10. What will be the cost of 5 pens, 8 pens and 10 pens?
Number of pens 1 5 8 10
Cost 10 50 80 100
Extremes
Means
