https's answer to Juliana's Primary 6 Maths Percentage Singapore question.

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Https's answer
57 answers (A Helpful Person)
Work backwards. Total unchanged. Internal transfer.

J : R
3 : 3
1 : 5
3 : 15
5 : 13

13u - 5u = 8u = 144
1u = 18
5u = 90 (Ans)