Can You Solve This Math Problem?

I love stories about people who didn’t give up. Miles Levin is such a story. Stories of perseverance help to motivate us in all aspects of our life, including our financial lives. But how do we teach perseverance to our kids? That was my challenge this weekend when my son was trying to solve a difficult math problem.

Using the numbers 1 through 9 in order, construct a math problem that equals 100.

Simple enough, right? If you can add, subtract, multiply and divide, you can solve this problem. When the answer didn’t come easily to him, he wanted to give up. But through encouragement (ok, and some threats, too), he worked through the problem and solved it. I told him that life is a series of problems, just like this one. And at each step in life, you have a choice–give up or keep trying. And we answer that question every day, whether we realize it or not.

So can you solve the math problem? Leave a comment if you think you’ve got the answer. Oh, and here’s a hint: You can use parentheses to change the order of operation.

Topics: Personal Finance

60 Responses to “Can You Solve This Math Problem?”

  1. Rob, well done. What I like about this math problem is how simple the solution appears. There are other ways to solve the problem, by the way, so leave a comment if you have figured out these other alternatives.

  2. Al Brockman

    I have three possible solutions – two from my son; one from my son-in-law. Here they are:
    100 = (1+2+3+4) x [(5-6) x 7 + 8 + 9]

    1-2*3-4+5*6+7+8*9 = 100. I like this because, though parentheses could be applied, you don’t need them if your order of operations is correct. I’m mucking around with something more creative (exponents are allowed, right?)

    I think I could come up with the simple ones with a C program (sigh – it was going to be a shell script, but C handles arrays better) — there are eight operands, and (presuming simple math plus exponents) five possibilities for each operand: + – * / ^, which means 5^8 combinations, or 390625. All you have to do is build a 390625 row array with eight columns, each row representing a possible combination. Then you run something that translates, say,

    1 1 1 1 1 1 1 1 into 1-2-3-4-5-6-7-8-9, and evaluates whether that equals 100.

    After that, it’s, as my high school geometry teacher would say, “just plug & chug”

  3. Sara, very nice. This “simple” math problem reminds me that there are often multiple solutions to the same problem or challenge. Money is the same way. There are definitely many wrong answers. But there are also several paths that each can get us to our goals.

    • Linda, the answer will depend in part on the rate at which the interest compounds (daily, weekly, monthly, annually). But that said, my answer for this and your other questions is (in round numbers) $324.34, $6.72 and $1.15.

  4. Erica

    You have been hired by a day care agency to fence in an are a to be used for a playground. You have been provided with 60 feet of fencing (in 4-foot sections) and a foot gate. How can you put up the fence so the children have the maximum amount of space in which to play?

  5. Alberto Munoz

    Dear Erica regarding your problem about the fence:
    You have to use a rectangle of maximun area i.e. a square , the perimeter is 60 feet of fencing plus 1 foot of gate: all together 61 feet, you build a square with a side of 61/4 each.

    • Found this on the internet. Thanks to someone. Here is 25 of the 199 answers he had.

      1 1/2*7+5*3*6/9+8*4
      2 1/2*7+5*6*3/9+8*4
      3 1/2*8+5*3*6/9+7*4
      4 1/2*8+5*6*3/9+7*4
      5 1/3*6+5*2*8/7+9*4
      6 1/3*6+5*8*2/7+9*4
      7 1/3*6+7*2*8/9+4*5
      8 1/3*6+7*8*2/9+4*5
      9 1/3*8+9*2*6/7+5*4
      10 1/3*8+9*6*2/7+5*4
      11 1/3*9+4*2*6/7+8*5
      12 1/3*9+4*6*2/7+8*5
      13 1/4*7+2*3*6/9+5*8
      14 1/4*7+2*6*3/9+5*8
      15 1/4*8+7*3*6/9+2*5
      16 1/4*8+7*6*3/9+2*5
      17 1/6*2+5*3*9/8+7*4
      18 1/6*2+5*9*3/8+7*4
      19 1/6*2+7*3*4/8+9*5
      20 1/6*2+7*4*3/8+9*5
      21 1/6*8+2*3*9/5+7*4
      22 1/6*8+2*9*3/5+7*4
      23 1/9*3+2*6*8/7+4*5
      24 1/9*3+2*8*6/7+4*5
      25 1/9*5+8*3*4/7+2*6

  6. Md. Badsha Faysal

    I have a book named “Foundations of Financial Management”.
    Author: Stanley B. Block and Geoffrey A. Hirt (12th Edition).

    In this book, there have a lot of problems of math. It has no solution. So, I need specific solution of Chapter-6: Working Capital & Financing Decision. Problems No: 7, 9, 10, 11, 12 & 13.

    If you provide me, I will be grateful to you.

  7. Md. Badsha Faysal

    Solve these problems that are given below.

    1. Stern Educational TV, Inc., has decided to buy a new computer system with an expected life at three years at a cost of $200,000. The company can borrow $200,000 for three years at 12% annual interest or for one year at 10% annual interest.

    a. How much would the firm save in interest over the three year life of the computer system if the one year loan is utilized, and the loan is rolled over (reborrowed) each year at the same 10% rate? Compare this to the 12%, three year loan.

    b. What if interest rates on the 10% loan go up to 15% in the second year and 18% in the third year? What would be the total interest cost compared to the 12%, three year loan.

    2. Assume that Atlas Sporting Goods, Inc., has $800,000 in assets. If it goes with a low-liquidity plan for the assets, it can earn a return of 15%, but with a high-liquidity plan the return will be 12%. If the firm goes with a short-term financing plan, the financing cost on the $800,000 will be 8%, and with a long-term financing plan, the financing cost on the $800,000 will be 10%.

    a. Compute the anticipated return after financing costs with the most aggressive asset-financing mix.

    b. Compute the anticipated return after financing costs with the most conservative asset-financing mix.

    c. Compute the anticipated return after financing costs with the two moderate approaches to the asset-financing mix.

    3. Lear, Inc., has $800,000 in current assets, $350,000 of which are considered permanent current assets. In addition, the firm has $600,000 invest in fixed assets.

    a. Lear wishes to finance all fixed assets half of its permanent current assets with long-term financing costing 10%. The balance will be financed with short-term financing, which currently costs 5%. Lear’s earnings before interests & taxes are $200,000. Determine Lear’s earnings after taxes under this financing plan. The tax rate is 30%.

    b. As an alternative, Lear might wish to finance all fixed assets and permanent current assets plus half of its temporary current assets with long-term financing and the balance with short-term financing. The same interest rates apply as in part b. Earnings before interests & taxes are $200,000. What will be Lear’s earnings after taxes? The taw rate is 30%.

  8. my math question :
    we have 1oo coins that one side them is white and the other side is black .
    we put 7 of the coins in white side and the others (93) in black side .
    now we want a blind person to divide the coins into X parts that the number of white coins in all the parts be the same .
    how can the blind person do that ?
    I will wait for your respond , thanks .

  9. marie jeanette zacarias

    adding and subracting fractions.. can you explain it to me how did you get the 14
    7/9 +1/8-1/6= 14/18+1/18-3/18

    can you explain it to me how you solve it thanks

  10. I need to solve this math problem …

    using numbers from 1 to 9 ( 1,2,3,4,5,6,7,8,9)

    __ __ X __ __ __ = __ __ __ __
    the numbers should not repeat, and it should be between 1 to 9 only.

  11. robert

    A surveyor measured a triangular plot of ground and reported three angles as being 58.2 degrees, 70.0 degrees and 61.1 degrees. How much of an error did the surveyor make?


    A developer sell 2 lots that are each 60 X 100 for $20 per square foot each. On the first lot she makes a 20% profit. On the second lot, she suffers a 20% loss. Calculate her net profit or loss.

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