GED Mathematical Reasoning: Money – Multiplying and Dividing

Example 1

Multiply $2.34 by 5.

 

We’ll multiply this as we would multiply the whole numbers 234 and 5.

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5 multiplied by 4 is equal to 20. Place the zero in the ones place and carry the 2 – writing it above the 3.

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Next, multiply 5 times 3 and then add the 2. The result is 17. Place the 7 in the tens place and carry the 1.

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Finally, multiply 5 times 2 and add the 1. The result is 11, which we write to the left of the 7.

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For our final answer, we will be sure to include the decimal point and dollar sign.

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Since there are two digits to the right of the decimal in the dollar amount given in the original problem ($2.34), we place the decimal point in our final answer so that there are two digits to the right of it. Therefore, our final answer is:  $11.70

Let’s pause to discuss the importance of evaluating an answer for reasonableness. When completing a math problem, it is beneficial to stop and ask ourselves: Does the answer seem reasonable given the original values? Evaluating an answer for reasonableness is a way to double check our work and catch mistakes we may have made. For example, is $11.70 a reasonable answer for $2.34 times 5?

Well, $2.34 is very close to $2. And if we multiply 2 by 5, we can quickly calculate the result to be 10. Since $2.34 is slightly higher than $2, we can expect the result of $2.34 times 5 to be slightly higher than $10. Since it is, at $11.70, we can feel confident that we did the problem correctly and our answer is right.

 

Example 2

Divide: $8.92 by 4

 

We will write this using the division bracket. The dividend of $8.92 goes underneath the bracket and the divisor of 4 sits outside to the left.

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Divide this as you would divide 892 by 4. Before you begin the long division process, bring the decimal point straight up – to sit on top of the division bracket directly above its current position. math 103

4 goes into 8 two times. Place a 2 on top of the division bracket, directly over the 8.

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Now we multiply – 2 times 4 equals 8. Place this product underneath the 8 of the dividend and subtract. 8 minus 8 equals zero.

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Although the remainder is zero, we continue on because there is a digit to bring down. Bring down the 9.

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Don’t let the zero throw you off, now we repeat the process using 09 – or just 9 – as our new dividend. 4 goes in to 9 twice. We write the 2 on top of the bracket, directly over the 9 and to the right of the decimal point.

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2 times 4 is equal to 8. Write the 8 underneath the 9 and subtract 8 from 9. The result is 1. Bring down the 2.

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Now repeat the process, using the number 12 as our new dividend. 4 goes into 12 three times. Write the number 3 on top of the bracket directly over the 2.

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3 times 4 equals 12. Write 12 underneath the 12 and subtract. Because the remainder is zero and there are no digits remaining to bring down, the process is complete.

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The final answer is: $2.23.

Now, does our answer make sense? $8.92 is very close to $8. And we can quickly calculate that 8 divided by 4 is 2. Since $8.92 is slightly higher than $8, we should expect $8.92 divided by 4 to be slightly more than $2. And it is at $2.23. So we can feel confident that we worked the problem correctly and that our answer is right.

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