Singapore Math Guru

30% to 40% of students get this type of question wrong!

It is amazing how many students get questions like these wrong!

Have you ever seen questions like:

What fraction of 5 km is 8000 m?

Or have you seen questions like:

What percentage of 2 litres is 3000 ml?

 

For the first question, the variety of answers range the gamut. Some students will give their answers  as 5/8 or even 5/8000 which is wrong. Just because 8000 is larger than 5000, that doesn’t make it the denominator.

The correct way to do it is this:road-368703_1280

1) Convert 5 km to 5000 m. Your child or student has to know how to do this first.

2) Then, let’s re-read the question.

What fraction of 5 km is 8000 m?

3) Let’s re-write the question.

Since we know that 5 km is 5000 m, the question can now be written as :

What fraction of 5000 m is 8000 m?

    Now, focus on what has been underlined.

    “of 5000 m” means take 5000 m to be your reference point. So, 5000 m must be your denominator.

Therefore, the fraction must be: 8000/5000

= 8/5

= 1 3/5 (1 and 3-fifth)

 

With regards to the 2nd question, you can do the same:

baby-bottle-147735_1280What percentage of 2 litres is 3000 ml?

1) Convert 2 litres to 2000 ml.

2) Now, the question reads as:

What percentage of 2000 ml is 3000 ml?

    2000 ml must be the denominator.

3000/2000 x 100% = 150%

So there you ago! Simple mistakes that can and must be avoided.

 

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