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Singapore Math

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Lily and Sara each had an equal amount of money at first. After Lily spent $18 and Sara spent $25, Lily had twice as much as Sara. How much money did each of them have at first?

  • Math -

    Let the amount each had initially be x.

    x - 18 = 2*(x - 25) = 2x - 50
    x = 32

  • Singapore Math -

    Here is your bar model:
    This is a unit bar: [xxx]

    Before - the had equal amounts, then they each spent some money. In the end, Lily has twice as much as Sara, or 2 units.

    Lily [xxx][xxx]<----$18---->|
    Sara [xxx]<-----$25-------->|

    If they started out the same, the second unit bar for Lily must be equal to $25 - $18, so $7
    Lily had 2 units (2 x $7)+$18 at first.
    Sara had 1 unit ($7)+$25 at first.

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