18

There are 66 cats in my street. I don’t like 21 of them because they catch mice. Of the rest, 32 have stripes and 27 have one black ear. The number of cats with both stripes and one black ear is as small as it could possibly be. How many cats have both stripes and one black ear?

A. 5

B. 8

C. 11

D. 13

E. 14

Answer

E. 14

SOLUTIOn

The information in the question tells us that the number of cats in my street that don’t catch mice is 66 − 21 = 45. Of these 45, let the number of cats with both stripes and one black ear be X and let the number of cats with neither stripes nor one black ear be Y. Since 32 cats have stripes and 27 have one black ear, we have 32 + 27 − X + Y = 45 and hence that 14 + Y = X. We are told that the number of cats with both stripes and one black ear is as small as possible and hence that number is 14 with no cats having neither stripes nor one black ear.

Subscribe to receive updates!

Be up-to-date with our recent updates, new problems and answers!

Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

Our courses

Get ready for olympiads with free problems, extracurricular topics and our courses

Mathematics

Programming

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 introductory 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.
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.
Hear from some of our amazing students who already achieved incredible results with us!
"Olympiad Maths Lessons helped me a lot to get the Gold medal in Junior Maths Challenge"
St. Paul's Student
"Thanks to the 'Data Science' and 'Coding in Python' lessons I got accepted to my dream university."
Michael
Data Science Student
Warwick University
"Great courses, which thoroughly explained topics beyond the capability of the GCSE answer sheet. Thanks so much."
Ivan
GCSE Student in Dubai
"Financial Mathematics! Best course to understand Python and Mathematics behind Finance!"
Gleb
VC Investor
"We got silver in PMC! Thanks George!"
Mum of St. Paul's Student
Prepare for the Primary Maths Challenge
"My daughter took a batch of 10 classes with George to understand Python with Turtle. I found George extremely knowledgeable and accessible."
Dad of Latymer School Student
Python with Turtle

Contact us

...or ask us anything

Ask about our courses and offerings, and we will help you choose what works best for you.

Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.