F.2 Mathematics (Ratio)

Letn be the number of pencils.

The number of black ball pensis twice the number of pencils.
Then, the number of black ball pens = 2n

The number of blue ball pens is 4 more than thatof black ball pens.
Then, the number of blue ball pens = 2n + 4

There are 24 pens in a pencil box.
n + 2n + (2n + 4) = 24
5n + 4 = 24
5n = 20
n = 4

(Number of blue ball pens) : (Numberof black ball pens) :(Number of pencils)
= (2n + 4) : 2n : n
= (2 x 4 + 4) : (2 x 4) : 4
= 12 : 8 : 4
= 3 : 2 : 1

一睇就知 001 個答案錯咗。

全部有 24 枝筆，若果數目比例係 8 : 2 : 1，即係全部筆嘅數目唔係整數，點會啱？

Let a be the number of black ball pens.
4a is the number of blue pens
1/2a is the number of pencil

the ratio of the number of blue ball pens to the number of black ball pens to the
number of pencils
=4a:a:1/2a
=8a:2a:a
=8:2:1