Mr Lim’s salary — amount saved
Mr Lim spent of his salary on household and medical expenses, with of the household expenses equal to of the medical fees. He gave of the remainder to his mother and saved the rest; his mother received $150 more than the medical fees. How much did he save?
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The pattern behind it: Branching
The second fraction is of one piece, not of the whole.
In this one. Use the same small unit throughout every branch so amounts from different branches can be compared directly.
How to spot it
A second fraction arrives after the first and is attached to a piece rather than to the whole — 'of the remainder', 'of what was left', or 'of the ones that were red'.
Common mistake
Children take the second fraction of the original total instead of the piece it was named against, which makes the amount come out too big.
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