Boys usually learn faster if they are hands on and can visualise the problems. As such, I usually use Legos to explain maths concept to my son so he can visualise the working and the solution.

Last night, we were going through the maths homework and there was this arithmetic problem sum that required the understand of the concept of units. It only dawned upon me in the morning after how I could have used Legos to explain the concept to him, which I will be showing him later today.

The Problem Sum

There are three fishes. Fish A cost three times as much as Fish B. Fish C cost $4 less than Fish B. The total cost of the three fishes is $46. Find the cost of Fish A. 

Step 1: Compare cost of Fish B and Fish A.

Let's take the 1-whole Lego block to represent the cost of Fish B.


Since Fish A cost three times as much as Fish B, the cost of Fish A cost 3 x 1-whole Lego Block.


Step 2: Compare cost of Fish B and Fish C

 As Fish C cost $4 less, let's the 3/4 Lego block to represent the cost of Fish C.


The $4 difference can be presented by the 1/4 Lego Block.

Step 3: Cost of 1-whole Lego Block

To find the cost of a 1-whole Lego Block, I will need to the cost of Fish B to be represented by a 1-whole Lego Block. This will then allow me to take the Total Cost of the Fishes to be presented by 5 x 1-whole Lego Blocks and I can divide this Total Cost by 5 to find out the cost represented by 1-whole Lego Block.

However, the cost of Fish C is short of a 1/4 Lego Block (=$4). As such, I have to add the 1/4 Lego Block to Fish C to make it a full 1-whole Lego Block.

If I add 1/4 Logo Block to Fish C, I would also need to add 1/4 Logo Block to the total cost.

Since the 1/4 Logo Block = $4, I add $4 to the total cost of the Fishes which is now $50.


Step 4: Determine the value of 1-whole Lego Block

The value of 1-whole Lego Block can be determined now by $50/5 = $10.

Since cost of Fish B is represented by 1-whole Lego Block, Fish B cost $10.

Step 5: Calculate the cost of Fish A

As the value of Fish A is represented by 3 x 1-whole Lego Blocks, cost of Fish A is $10 x 3 = $30.

The question could also ask to find of cost of Fish C. To do this, simply take $10 - $4 = $6 as from the block diagrams.


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