Not a good idea to use algebraic approach. Bear in mind that the question is posted as a Primary 4 question.

What would your answer be then?

You will need to use the assumption method (practically guess and check) at the Primary 4 level. Using algebraic expressions like x and y is more appropriate for a Secondary 2 student.

I know you have tried to explain the equation in the simplest of way to the student, but then again. the level gap is still too big.

Perhaps if you used "units" and "parts" instead of x and y, they might be able to absorb the terms better. But then again, if I recall, "units" and "parts" are used together only at the Primary 5 or at the Primary 6 level.

----------------------------------------------

A bicycle has 2 wheels.
A tricycle has 3 wheels.

Assume that all 47 cycles are bicycles.

Number of wheels for 47 bicycles
= 47 x 2
= 94

But there are 115 wheels. So, there cannot be 47 bicycles.

Replacing a bicycle with a tricycle keeps the number of cycles the same, but increases the number of wheels by 1.

To get 115 wheels, we need to add 21 wheels altogether. This means a total of 21 bicycles have to be swapped to tricycles, leaving behind 26 bicycles.

Therefore, there are 21 tricycles and 26 bicycles.

Check:

Number of wheels from tricycles
= 21 x 3
= 63

Number of wheels from bicycles
= 26 x 2
= 52

Total number of bicycles
= 63 + 52
= 115

The students at Primary 4 use the assumption method to solve such questions, often presented in a table format.