This lesson will show you how to solve four word problems related to the multiplication of integers.
Problem #1
From sea level, a submarine descends 40 feet per minute. Where is the submarine in relation to sea level 5 minutes after it starts descending?
Solution
In 1 minute, the submarine is 40 feet below sea level or at -40 feet. We use a negative sign since the submarine is descending.
After 5 minutes, the submarine is at -40 × 5 = -200 feet
Problem #2
The price of one share of a stock fell 4 dollars each day for 8 days. How much value did one share of the stock lose?
Solution
Each day, one share of the stock goes down by 4 dollars. We can represent this situation with the integer -4.
After 8 days, one share of a stock has gone down by -4 × 8 = -32
One share of a stock is now worth 32 dollars less.
Problem #3
A test has 20 questions. The test awards 3 points if the answer is correct and takes away 1 point if the answer is incorrect. A student answered 5 questions incorrectly. How many points did the student lose?
Solution
For each incorrect answer, the student earns -1 point.
After answering 5 questions incorrectly the student earns -1 × 5 = -5.
The students lost 5 points.
Problem #4
A credit card company charges a late fee of 25 dollars each time a customer fails to pay on time. A customer missed the payment 4 times last year. At the customer's request and out of courtesy, the credit card company decides to cancel all late fees for that year. Write a numerical expression to show how much money was return.
Solution
The amount of late fee the bank charged last year was -25 × 4
In order to return the money, the bank can do this math: -25 × -4
Notice how the number 4 became negative. This is necessary so the amount of money the customer gets back is a positive number.
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