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Upper primary school mathematics question UPQ136
Teacher in charge of the event prepared a box of pens and pencils to use in the school anniversary event. If the teacher took out 140 pencils, 1/3 of the remaining items in the box were pencils. If the teacher took out 25% of the pens, then ¼ of the remaining items in the box were pens.
(a) How many pens were there in the box at first?
(b) How many pencils were there?
Draw the math model based on the above two ‘if’s.
To note that the number of pens and pencils are constant
25% of the pens ==> 1/4 of the total number of pens
From the model,
7 units = 140
1 unit = 20
Pens in the box at first = 4 × 20 = 80
Pencils in the box = 9 × 20 = 180