103

A student made an error while multiplying two three-digit numbers. Instead of noticing the multiplication sign between them, the student wrote the numbers together, forming a six-digit number.

Surprisingly, this mistake resulted in a product that was three times greater than the actual product of the two numbers.

Can you find these two original three-digit numbers?

Answer

A = 167,  B = 334.

SOLUTIOn

We start by assigning variables to the two three-digit numbers: let A represent the first three-digit number and B represent the second. According to the given condition, if we mistakenly combine these numbers, forming a six-digit number, we get 1000A + B. Surprisingly, this erroneous expression equals three times the actual product of the two numbers, which gives us the equation 1000A + B = 3AB.

Rearranging this equation, we get (3A - 1)B = 1000A. Since A and 3A - 1 are coprime, we deduce that 1000 must be divisible by 3A - 1.

Considering the possible values for 3A - 1, we recognize that it must be a three-digit or four-digit number since A is a three-digit number. Therefore, 1000 has two potential divisors fitting this criterion: 500 and 1000.

However, 3A - 1 cannot equal 1000 because 1001 (which is 3A) is not divisible by 3. Thus, we deduce that 3A - 1 must equal 500. Solving this equation, we find that A equals 167. Substituting this value back into the original equation, we can solve for B, which equals 334.

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FAQ

Find quick answers to common questions about our lessons, pricing, scheduling, and how Exact Science can help your child excel.
Where do you hold your classes?
We hold our classes online or on-site on Saturdays at our branch in Pimlico Academy, London.
You can find our timetable here.
What do you need to start learning online?
For lessons you only need a computer or phone with a microphone, camera and Internet access. Wherever you are - in London, Nottingham, New York or Bali - online lessons will be at hand.
When can I take the trial lesson?
You can get acquainted with the school at any time convenient for you. To do this, just leave a request and sign up for a lesson.
What should I expect from the trial lesson?
The trial lesson is a 30-minute online session designed to get a sense of how your child approaches mathematical thinking and problem solving. (In practice, it often runs a bit longer if the student is engaged!)

We typically explore a range of fun and challenging problems drawn from competitions. We adapt the difficulty based on how the student responds, aiming to make it both accessible and stimulating.

After the session, we’ll have a quick conversation with the parent to share observations and suggest a personalised path forward.
I can't attend class, what should I do?
It is OK, it happens! Students have the opportunity to cancel a lesson up to 8 hours before the scheduled time without loss of payment. So you can reschedule it for a convenient time, and the teacher will have the opportunity to
I don't have much free time, will I have time to study?
Learning can take place at your own pace. We will select a convenient schedule and at any time we will help you change the schedule, take a break or adjust the program.
How long is one lesson?
All classes last 1 hour.

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