PS/IS 686 | Brooklyn, NY

Grade 4 Math: Estimation vs. Rounding

Estimation?  Rounding? What’s the difference?  Many people think there’s no difference.  While they are related, and rounding can be used  to assist in estimation, there are differences. Both rounding and estimation are used when an exact answer isn’t needed.  However, rounding is very digit specific, while estimation may not be.  For example, if I were to round the number 561, I need to round it to a particular place.  If I round it to the tens place, I will get 560.  If I round it to the hundreds place, I will get 600, and if I round it to the thousands place, I will get 1000.

Estimation is a little more nuanced.  Estimation involves looking at the entire number and deciding what makes sense in the situation.  If I’m thinking about what two groups of 561 would approximately be, I may not choose to round at all.  I might notice that two 500s are 1000, so I know my total would be over 1000.  Estimation also doesn’t necessarily involve what we traditionally call “friendly numbers” (numbers that end in 0).  If I am combining numbers such as 77 and 27, I may think about landmarks related to money and not do any rounding.  I would think 75 and 25 are 100, so I would know my total would be close to 100.

Students received their math tests back on Monday.  There were a few trends that I noticed that I would like to share with both you and the students.  One is checking to be sure an answer makes sense.  If I’m subtracting 338 – 56, can my answer be greater than 33?  The second  is dollar and cents notation.  I will be reviewing with the students that we don’t use both the dollar and cents signs together.  If I have 3 dollars and 25 cents, I can write $3.25, which is equivalent to 325¢, but I can’t write 3.25¢, since that means 3 and a quarter cents. Also, we don’t typically write $3.25¢.  It is unclear hear what the meaning of the symbols is.

We are now moving into multiplication and are reviewing factors and arrays.  Have a great week!