Mathematics Magazine for Grades 1-12  

4/2004

If the temper of your mind gets interwoven with your convictions, you lose in heat what you might gain by reason.
 - Margot Asquith

Grade 3

Theory: 

Estimating by front end estimation

Front-end estimation generally produces a better estimate of sums or differences than rounding before adding or subtracting.

How to Estimate a difference by front-end estimation

Subtract the digits of the two highest place values

Insert zeros for the other place values

Example: 7396 minus 3745 is estimated to be 3600 by front end estimation (i.e. 7300-3700).

Solutions from the Previous Issue:

Transform:

1.        400 dl = ? l

Solution:  400 dl = 40 l

2.        180 cl = ? dl

Solution:  180 cl = 1800 dl

3.        6400 cl = ? dl

Solution:  6400 cl = 640 dl

4.        103 dl = ? cl

Solution:  103 dl = 1030 cl

Proposed Exercises:

Calculate:

1.        27 + 39 – 18 =

2.        81 – 38 + 28 =

3.        75 – 36 + 48 =

4.        86 – 38 + 29 =

5.        (6 x 8) + (9 x 3) =