Sunday, October 3, 2010

Decimal P6 2010 SA2 Nanyang P2 Q13

Quiny and Mandy saved $5748.40 altogether. 0.4 of Quiny’s savings was $431.50 more than 0.2 of Mandy’s savings. How much more money than Quiny did Mandy save? [4 marks][Answer given: $477.80]


Quiny's money --> 10 Q
Mandy's money --> 10M
4 Q --> 2 M + $431.50

2 M --> 4 Q - $431.50

10 M --> 20 Q - 5 x 431.50 = 20 Q - $2157.50


10 Q + 10 M --> $5748.40

30 Q --> 5748.40 + 2157.50 = 7509.90

10 Q --> 7509.90/3 = $2635.30

10 M --> 2 x 2635.30 - 2157.50 = $3113.10

10 M - 10 Q --> 3113.10 - 2635.30 = $477.80

It was $477.80.


Model Drawing
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431.50 / 2 = $215..75   0.4 = 4/10 = 2/5

Compare 2 units of Q (total 5 units) with 2 units of M (total 10 units)
Q  [][215.75][][          ][][           ][][            ][][             ]   ] $5748.40
M [][][][][][][][][][]                                                            ]

215.75 x 5 = 1078.75

15 u --> 5748.40 - 431.50 = 4669.65

5 u --> 5/15 x 4669.75 = 1556.55

1078.75 - 1556.55 = $477.80

It was $477.80.

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