myQBook

Aug 2, 2024

Answers to Real World Examples of Number Sense

In our last blog, we provided some real-world problems for you to test your number sense skills. In this blog, we explain the number sense methods to solve those problems and provide their answers.
The first problem we posed in the last blog was to figure out how to divide the total bill of $135 ($108 + 25% tip of $27) among 5 people. There are multiple ways of solving this problem using number sense. The first one of course is to break $135 into two parts of $100 and $35 and divide each part into 5. So, $100/5 = $20 and $35/5 = $7 and hence each person will pay $27.
Another way to solve this problem is to realize that when you calculated 25% tip ($27) and added it to the bill amount of $108, the total amount became 125% of the original bill. Since there are five 25% in 125%, there are also five $27 in the total. So, each person will pay $27.
Here are the answers to the other real-world examples in the previous blog.
  • Discounts and Sales:
    • If an item is originally priced at $80 and is on sale for 30% off, what is the sale price?
    • Number Sense Method:
      • The quickest way to solve this problem is to first figure out 10% of $80 = $8.
      • Now, there are two ways to come up with the answer:
        • One is to realize that if an item is 30% off that means the item is selling at 70% of the original price. So, if 10% is $8, 70% would be $8 x 7 = $56.
        • The other way is to first calculate 30% and then subtract it from $80. So, if 10% is $8, 30% would be $8 x 3 = $24. Hence the selling price is $80 - $24 = $56.

  • Time and Distance:
    • A train travels at an average speed of 50 miles per hour. How long will it take to travel 175 miles?
    • Number Sense Method:
      • The quickest way to solve this problem is to first figure out how many 50s are there in 175 miles. Since 3 x 50 is 150, we know there are 3 full 50s and the remainder is 25 miles. And 25 is half of 50. So, there are 3 and ½ 50s in 175.
      • So, if the average speed is 50 miles per hour, it will take 3 and ½ hours to travel 175 miles.

  • Proportions and Scaling:
    • If a recipe calls for 2 cups of flour to make 24 cookies, how much flour is needed to make 42 cookies?
    • Number Sense Method:
      • The quickest way to solve this problem is to first figure out how many cookies can be made with 1 cup of flour. If 2 cups of flour will make 24 cookies, then 1 cup will make 12 cookies.
      • Now figure out how many 12s are there is 42. Since 12 x 3 = 36 we know there are 3 full 12s and the remainder is 6. And 6 is half of 12. So, there are 3 and ½ 12s in 42 cookies.
      • So, if 1 cup makes 12 cookies, 3 cups will make 36 cookies and 3 and ½ cups will make 42 cookies.

  • Interest and Investments:
    • If you take a loan of $50,000 at an annual interest rate of 6%, how much interest will you pay in 3 years?
    • Number Sense Method:
      • The quickest way to solve this problem is to first figure out what is 1% of $50,000. 1% (which means 1 out of 100) of $50,000 is $500 (divide 50,000 by 100).
      • If 1% if $500, then 6% will be 6 x $500 = $3000.
      • Since the annual interest rate is 6%, you pay $3000 each year. Hence in 3 years you will pay $3000 x 3 = $9000.

  • Measurement and Conversions:
    • You are 5.5 feet tall. How tall are you in inches?
    • Number Sense Method:
      • The quickest way to solve this problem is to first realize that there are 12 inches in a foot.
      • So, 5 feet will be 5 x 12 = 60 inches, and 0.5 feet (half a foot) is 6 inches.
      • Hence, 5.5 feet is 66 inches.
Why Developing Number Sense is Important
  1. Strong foundation for higher-level math: Number sense is the building block for more complex mathematical concepts like algebra, geometry, and calculus. A student with strong number sense can more easily grasp abstract ideas and solve problems.
  2. Real-world problem-solving: Number sense enables individuals to apply mathematical skills to everyday situations, such as calculating discounts, comparing prices, understanding statistics, and making financial decisions.
  3. Critical thinking and reasoning: Number sense encourages students to think critically, analyze information, and develop problem-solving strategies. It fosters a deeper understanding of mathematical relationships and patterns.
  4. Mental math proficiency: Number sense enhances mental math abilities, allowing individuals to perform calculations quickly and accurately without relying solely on calculators or written methods.
myQBook offers an industry leading number sense development program with more than 350 concepts and thousands of example problems. By learning and practicing just two concepts from the myQBook Number Sense program every week, students can develop a deeper understanding of numbers, enhance their problem-solving skills, and foster a lifelong appreciation for math.
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