## Monday, March 9, 2015

### [Pri20150308CSR] Charitable Savings Ratios?

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: Sharon’s savings was \$240 at first.

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