Mathematics
Intermediate Mathematical Challenge
2024
5

5

The ages of Grannie’s seven grandchildren are consecutive positive integers.

The youngest three grandchildren have a mean age of 6.

What is the mean age of the oldest three grandchildren?

A. 8 B. 9 C. 10 D. 11 E. 12

Answer

C. 10

SOLUTIOn

Because the mean age of the three youngest grandchildren is 6, and their ages are consecutive integers, their ages are 5, 6 and 7. It follows that the ages of all the seven grandchildren are 5, 6, 7, 8, 9, 10, 11, So the ages of the three oldest grandchildren are 9, 10, 11. Hence their mean age is 10.

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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.
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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
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All classes last 1 hour.

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