**Question**

**Introduction**

Here is
another one of those Singapore Mathematics problems that are two-variable
simultaneous equations in disguise. The
key to solving this question quickly is to exploit the fact that the amount of
donations are the same in this case.

**Solution**

First, read
the question and translate the information into a diagram [H02. Use a diagram / model]. I use different shapes (e.g. circle and
square) to envelop the different types of units.

Since we
have ‘-80’ for both Sharon and Ryan [H04. Look for pattern(s)], we may deduce that 1
‘circle’ unit (5 minus 4 ‘circle’ units)
is equal to 3 ‘square’ units (10 minus 7 ‘square’ units). That means 5 ‘circle’ units is 15 ‘square
units’. [ H10.
Simplify the problem]

By
comparison again, we realise that 5 square units is 80 [H05.
Work backwards] and hence 15 ‘square’ units is 240.

**Ans:**

**Check**

Before
$240 $192 5 : 4

After
$160 $112 10 : 7

Solution makes sense.

H02. Use a diagram / model

H04. Look for pattern(s)

H05. Work backwards

H10. Simplify the problem
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