Mathematics
Grey Kangaroo
2022
4

4

In the equation on the right there are five empty squares. Sanja wants to fill four of them with plus signs and one with a minus sign so that the equation is correct. Where should she place the minus sign?

A. Between 6 and 9 B. Between 9 and 12 C. Between 12 and 15 D. Between 15 and 18 E. Between 18 and 21

Answer

D

SOLUTIOn

The value of 6 + 9 + 12 + 15 + 18 + 21 is 81. Now 81−45 = 36 = 2×18. Therefore, Sanja needs to subtract rather than add 18 and hence the minus sign should be placed between 15 and 18.

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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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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.

What our students and parents say about learning with us

"Olympiad Maths Lessons helped me a lot to get the Gold medal in Junior Maths Challenge"
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Warwick University
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Prepare for the Primary Maths Challenge
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