Primary 4 GEP

by Joyce sim
(Singapore)

Average of a number of files is $4. After buying another file which cost $16, the average increases to $7. Find the number of files at the beginning.

Here's My Answer
by Zach
(Singapore)

Step 1: This question involves the Total Vs Individual Difference Concept. First, we draw 1 box to represent the old average of $4. Then we draw an arrow to the right to show that this box is repeated by an unknown number of times (label "?" at the end of the arrow).

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