P5 Math: Asmidah spent

Asmidah spent 7/9 of her money on 6 files, 10 pens, and 15 rulers. She could buy 4 pens and 6 rulers with the remaining money but she spent all of it on files instead. How many files could Asmidah buy with the remaining money ?

Solution:

In a model, total is 9 units.

• 7 units for 6 files + 10 pens + 15 rulers --> 7u = 6f + 10p + 15r
• 2 units for 4 pens + 6 rulers --> 1u = 2p + 3r --> 5u = 10p + 15r

We can deduce from two facts above that 2u equals to 6f.

It means 2 units (which is the remaining money) can be used to buy 6 files.