Math Reminders

When we don't use our math skills very often, we forget how to figure certain things out!

My 6th-grade son Michael and I have been putting together these
Math Reminders
as a quick visual aid to help kids and grown-ups recall some basic math facts.

Math Problem

How to Approach the Problem

Line up the decimal points:

Count the number of digits after the decimal points in the problem.
That's how many digits after the decimal point in the answer:

Convert 0.03 to a whole number:

Then do the division:

Math Problem

How to Approach the Problem

Divide the top and bottom by the same number:

Remember, if you do something to the bottom number,
always do the same thing to the top number!

Find common denominators for:

In this example we can multiply the bottom of the
first fraction by 5 so that it is the same as the
bottom of the second fraction:

Remember, if you do something to the bottom number,
always do the same thing to the top number!

So the answer is:

Find common denominators for:

The simplest way to find a common denominator is to
multiply the two bottom numbers (2 and 5).
Therefore, multiply the denominator of each fraction
times the denominator of the other fraction:

Remember, if you do something to the bottom number,
always do the same thing to the top number!

So the answer is:

Convert this improper fraction
to a mixed number:

Convert this mixed number
to an improper fraction:

One method is to convert the 2 into a fraction
and add it to the one-third:

Here's a quicker method. Multiply the 3 times the 2 and
add the 1, which equals 7:

Use the result (7) as the numerator, and put it over
the original denominator (3):

Find common denominators (the bottom numbers)
as shown above:

Then add the top numbers (the numerators):

Find common denominators (the bottom numbers)
as described above:

Then subtract the top numbers (the numerators):

Find common denominators (the bottom numbers)
as described above, and write the equation as a
subtraction problem:

We can't subtract six-tenths from five-tenths, so we
need to borrow from the 4 and add it to the five-tenths.
Notice that borrowing one from the 4 is the same as
borrowing ten-tenths so that we can add it to the
five-tenths:

Now we can do the subtraction:

Multiply the tops (the numerators),then
multiply the bottoms (the denominators):

Multiply four times five:

Then multiply four times two-thirds (as described above):

Add the two results together, then simplify the fraction:

Flip the second fraction over:

Then multiply (as described above):

Multiply (as described above):

Then divide:

Math Problem

How to Approach the Problem

Examples of converting between percents,
fractions, and decimals:

Math Problem

How to Approach the Problem

What are the perimeter and area of this square?

For the perimeter, add up all of the sides:

6 + 6 + 6 + 6 = 24 yards

For the area, multiply the length times the width:

6 x 6 = 36 square yards

What are the perimeter and area of this rectangle?

For the perimeter, add up all of the sides:

18 + 8.5 + 18 + 8.5 = 53 miles

For the area, multiply the length times the width:

18 x 8.5 = 153 square miles

What is the length of the hypotenuse (the diagonal
side) of this right triangle?

The square of the hypotenuse equals the square
of one side plus the square of the other side:

What are the perimeter and area of these triangles?

For the perimeter of a triangle, add up all of its sides:

The perimeter of the first triangle is the length of
the base (b) plus the length of side 1 (s1) plus
the length of side 2 (s2).
The perimeter of the second triangle is 3 + 4 + 5 = 12 cm.
The perimeter of the third triangle is 6 + 5 + 5 = 16 cm.

For the area of a triangle, multiply the base times the height, then
divide by 2:

The area of the first triangle is the base (b) times the
height (h) divided by 2.
The area of the second triangle is (3 x 4) divided by 2 = 6 sq. cm.
The area of the third triangle is (6 x 4) divided by 2 = 12 sq. cm.

What are the perimeter and area of this parallelogram?

For the perimeter, add up all of the sides:

27 + 12 + 27 + 12 = 78 inches

For the area, multiply the base times the height:

27 x 7 = 189 square inches

What are the perimeter and area of this trapezoid?

For the perimeter, add up all of the sides:

32 + 12 + 26 + 9 = 79 inches

For the area, add up the lengths of the two
parallel sides, then multiply the result times the
height, then divide the new result by 2:

((32 + 26) x 7) divided by 2 = 203 square inches

What are the radius, diameter, circumference, and
area of this circle?

The radius (the distance from the center to the outside
of the circle) is shown in the picture:

6 cm.

The diameter (the distance from one side to the other side
of the circle) is the radius times two:

6 x 2 = 12 cm.

The circumference (the "perimeter" of the circle)
is the diameter times pi:

12 x 3.14 = 37.68 cm.

The area is the radius squared times pi:

6 x 6 x 3.14 = 113.04 sq. cm.

We hope these Math Reminders are helpful, and if you have any suggestions then please let us know!

You'll find a Christian ministry with dozens and dozens of articles and answers to many questions that I have received over the years (please feel free to send me your questions and prayer requests!); plus a collection of some of the best self-working card tricks around (no sleight-of-hand required!); plus instructions and pictures which show you how to tie dozens of the most useful rope knots; plus a bunch of amazing/funny/fascinating/interesting videos from around the Web which are all clean and family-friendly; plus lots of reviews of numerous fun and educational (and free!) computer games that you can download; plus a huge collection of cool science tricks and other fun stuff to try (using things around the house), and more!

Modification History

02/12/2007:	Added a link to my new page called "Dave's Websites."
07/05/2006:	The whole family pitched in to give the website a bit of a facelift.
06/22/2006:	Added Fractions. Added Percents. Added Perimeter/Circumference/Areas. Added a printer-friendly version of each section.
05/21/2006:	New website.