CY Lew's answer to Lycia's Primary 6 Maths Ratio Singapore question.

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CY Lew
Cy Lew's answer
89 answers (A Helpful Person)
1st
Draw the model and make 1 unit of boys n girls = b and g respectively
From the model diagram, compare the before n after scenes, gives

3b = g + 310 gives g = 3b - 310 and 3g = 9b - 930
Next,
2b = 3g - 50
2b = 9b - 930 - 50
b = 140
Boys in the end = 140 x 2 = 280