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Not so sure with the syllabus, but saw it has algebra. you may use model to replace if need. 

Answer:

In order for Mr Ng to have 1/2 of his muffins chocolate, he needs to give at least 110+x chocolate muffins and x strawberry muffins (to end up with 90-x chocolate and 90-x strawberry)

Mr Loke will thus have 190+x chocolate muffins, and 100+x strawberry muffins. 

190+x = 3y (3 portions) — (1)

100+x = 2y (2 portions) — (2)

resulting in y=90 [above (1)-(2)]

100+x = 2(90) = 180, thus x =80

Mr Ng gave a total of 110+80 chocolate muffins and 80 strawberry muffins (total of 270 muffins given)