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Example 2<br />
Multiplying <strong>Rational</strong> <strong>Number</strong>s to Solve Problems<br />
On February 5, 2008, the price of a share in CIBC changed by $1.640.<br />
A person owns 35 shares. By how much did those shares change in value that day?<br />
Solutions<br />
Method 1<br />
Change in value:<br />
$1.640 35<br />
Since the rational numbers have opposite signs,<br />
their product is negative.<br />
To determine the product: (1.64)(35),<br />
multiply integers, then estimate to place the<br />
decimal point.<br />
(164)(35) 5740<br />
Estimate to place the decimal point:<br />
Since 1.64 is close to 2, then<br />
(1.64)(35) is close to (2)(35) 70.<br />
So, place the decimal point after the 7 in 5740.<br />
$1.640 35 $57.40<br />
The shares lost $57.40 that day.<br />
Method 2<br />
Change in value:<br />
$1.640 35<br />
Use a calculator.<br />
Key in 1.640 35 to display: 57.4<br />
$1.640 35 $57.40<br />
The shares lost $57.40 that day.<br />
Since the rational numbers<br />
have opposite signs, their<br />
product is negative, so we<br />
do not need to enter the<br />
negative sign.<br />
Example 3<br />
Multiplying <strong>Rational</strong> <strong>Number</strong>s in Decimal Form<br />
Determine each product.<br />
a) (0.8)(2.4) b) (1.25)(2.84)<br />
A<br />
Solution<br />
a) (0.8)(2.4)<br />
Since the rational numbers have opposite signs, their product is negative.<br />
Use mental math to determine the product:<br />
(8)(24) 192<br />
Estimate to place the decimal point:<br />
Since 0.8 is close to 1 and 2.4 is close to 2, then<br />
(0.8)(2.4) is close to (1)(2) 2.<br />
So, place the decimal point after the 1 in 192.<br />
Then, (0.8)(2.4) 1.92<br />
126 UNIT 3: <strong>Rational</strong> <strong>Number</strong>s
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