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MUST-KNOW PSLE MATH PROBLEM 1
April 9, 2016
The ratio of Eric’s money to Kim’s money was 3 : 1. After Eric gave Kim $60, the ratio of Eric’s money to Kim’s money became 3 : 5. How much did Eric have at first?
Solution using the Storyline-Balance Method:
E : K
At start: 3u : 1u
Story: – 60 + 60
At end: 3u – 60 1u + 60
Final ratio: 3 : 5
So 5 sets of (3u - 60) = 3 sets of (1u + 60)
15u – 300 = 3u + 180
15u – 3u = 180 + 300
12u = 480
1u = $40
So at first Eric had 3u = 3 x 40 = $120
The above is just one method. Another method requires you to notice that in the above problem, the total number of units remain the same as it is an INTERNAL TRANSFER or TOTAL UNCHANGED situation or concept. However, using the Storyline-Balance method, you don’t need to know what has been unchanged.