- One Quantity Unchanged Concept
- Constant Part Concept
- External Transfer (Unchanged Quantity) Concept
Whatever it is called, what is important is that one quantity remains the same, so we can use it to help us solve the sum.
Example1:
There are 40 pupils in a club. 40% of the pupils are boys. Some of the boys left the club, after which the percentage of boys in the club dropped to 30%. How many boys left the club?
Note: The number of girls remain the same.
Change 40% : 60% to their simplest form,
which is 2 : 3
Also 30% : 70% = 3: 7
Since the number of girls doesn’t change,
We want to make 3a and 7b to have the same
units.
We use LCM to get 21c for both Before and After.
35c à 70
1c à 70 ÷ 35 = 2
14c – 9c = 5c
5c
à 5 × 2 = 10 Ans: 10 boys left the club
Example2:
Sally had ⅞ as many brown eggs as white eggs. If she were to buy another 44 brown eggs, she would have ¾ as many white eggs as brown eggs. How many eggs did she have altogether?
We use LCM to get 24c
for both Before and After.
32c – 21c = 11c
11c à 44
1c à 44/11 = 4
45c à 45 x 4 = 180 Ans:
180 eggs
