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Thursday, October 02, 2008

PSLE Math Q on ratio

Andrea has \$200 more than Bala. Andrea gives 60% of his money to Bala. Bala then gives 25% of his money to Andrea. In the end, Bala has \$200 more than Andrea. How much did Andrea have at first? (Nanyang Prelim 2006 Q48)

At first -----
Andrea ----- 1 unit + 200
Bala ----- 1 unit

Andrea gives 60% -----
Andrea ----- 1 unit + 200 – 0.6 unit – 120
Bala ----- 1 unit + 0.6 unit + 120

Andrea ----- 0.4 unit + 80
Bala ----- 1.6 units + 120

Bala gives 25% -----
Bala ----- 1.6 units + 120 – 0.4 unit – 30
Andrea ----- 0.4 unit + 80 + 0.4 unit + 30

Bala ----- 1.2 units + 90
Andrea ----- 0.8 unit + 110

Bala now has \$200 more -----
Bala – Andrea ----- 200
1.2 units + 90 – 0.8 unit –110 ----- 200
0.4 unit – 20 ---- 200
0.4 unit ----- 200 + 20 = 220
1 unit ---- 220 divided by 0.4 = 550

Andrea at first -----
1 unit + 200 ----- 550 + 200 = 750

Anonymous said...

Hi Teacher,

There seems to have a confusion here.

Andrea has \$200 more than Bala. Andrea gives 60% of his money to Bala. Bala then gives 25% of his money to Andrea. In the end, Bala has \$200 more than Andrea. How much did Andrea have at first?
How did you derive the 120?

The question above stated that Andrea gives 60% of his money....

But how come you use the 60% * 200?

This part is quite confuse...Are you using assumption?

Another confusing part is when you minus 0.6 units,,,

I am totally clueless....

Excel Eduservice said...

Andrea had 1 unit + 200 at first.
If Andrea gives 60%, then ….

1 unit x 60% = 0.6 unit
200 x 60% = 120
Therefore Andrea gave away 0.6 unit and 120, which means….

What Andrea had at first – What Andrea gave -----
1 unit + 200 – 0.6 unit - 120

Anonymous said...

Thanks Teacher....I get picture,,,