How to solve Primary 4 heuristic problem sums involving "all change"?
Out of all the types of "Before-Change-After" problem sums, the more challenging ones are those that have no common base between the "before" and "after" status. This is the case when the values of the elements are changed. Below is an example of such question.
Bag A and Bag B had an equal amount of flour. Peter added 142 kg of flour in Bag A and removed 28 kg of flour from Bag B. As a result, the mass of the flour in Bag A became 6 times the mass of flour in Bag B. Find the mass of the flour in each bag at first?
15 units = 28 + 142 = 170
1 unit = 170 ÷ 5 = 34
34 + 28 = 62
The mass of each bag at first is 62 kg.