Transcript MTH 232

MTH 232
Section 7.2
Computations with Decimals
Objectives
1. Be able to round a decimal number to an
indicated value.
2. Be able to add and subtract decimals.
3. Be able to order decimals.
4. Be able to multiply decimals.
5. Be able to divide decimals.
Rounding Decimals
• The algorithm for rounding decimals is the
same as rounding whole numbers (refer to
Section 3.4 if you need a refresher), with one
notable exception: you do not add zeroes
after the rounded digit.
• For example, 364 rounded to the nearest ten
is 360, but 36.47 rounded to the nearest tenth
is 36.5.
Adding and Subtracting Decimals
• Adding and subtracting decimal numbers can
be modeled in a manner similar to adding and
subtracting whole numbers by using base-ten
blocks or ten-dollar bills, dollar-bills, dimes
and pennies.
• Algorithmically we write the problem in
vertical style, lining up the decimal points.
• Be sure to reinforce and use estimation and
mental calculation as well.
Examples:
Ordering Decimal Numbers
1. First, compare the integer parts of the two
numbers (the part to the left of the decimal
point), if any.
2. If the integer parts are the same, or if there
are no integers parts, start at the tenths
place and compare digits.
3. Moving to the right, keep comparing until
one digit is greater than the other.
Examples:
Multiplying Decimals
• To multiply two decimals, do the following:
1. Multiply as with integers.
2. Count the total number of digits to the right
of the decimal points of each number. Call
that number t.
3. Starting at the right of your product, move
the decimal point t places to the right.
Again, use estimate and mental calculation.
An Example:
Dividing Decimals
1. Move the decimal point in the divisor until
the number becomes an integer (no digits to
the right of the decimal).
2. Move the decimal point in the dividend the
same number of places.
3. Divide as with whole numbers.
Again, use estimation and mental computation.
Example: