Habs maths 2011 - question 30 can't do it

11 Plus Maths – Preparation and Information

Moderators: Section Moderators, Forum Moderators

Post Reply
11 Plus Platform - Online Practice Makes Perfect - Try Now
Minesh
Posts: 89
Joined: Sun Jul 18, 2010 9:02 pm

Habs maths 2011 - question 30 can't do it

Post by Minesh »

square is 3 units long with 4 identical semi-circles drawn on each edge. semi-circles overlap to create 4 petals which are shaded

the area of each semi-circle is 3.5 square units. work out shaded area

sorry can't draw
Victoria203
Posts: 20
Joined: Wed Oct 19, 2011 10:18 pm

Re: Habs maths 2011 - question 30 can't do it

Post by Victoria203 »

Area of Square = 3 X 3 = 9 square units
Total Area of all semi Circles = 3.5 X 4 = 14 square units

So, Area of shaded portions = 14 - 9 = 5 square units
Minesh
Posts: 89
Joined: Sun Jul 18, 2010 9:02 pm

Re: Habs maths 2011 - question 30 can't do it

Post by Minesh »

thanks for reply

i know i did not draw it but i don't think this is correct

am i wrong twice :oops: :mrgreen:
workhard
Posts: 132
Joined: Sat Jul 31, 2010 4:31 pm

Re: Habs maths 2011 - question 30 can't do it

Post by workhard »

Hi Minesh!

I just looked at the diagram (on Habs web site) until I noticed that I could calculate the unshaded area in this way:

Look at two opposing semi circles and imagine them completely shaded. Their area total 3.5 x 2 =7. What's left? It's the two bits opposite each other, which must total 9 - 7 = 2 in area.

There are two of these unshaded pairs of shapes, so the total unshaded area is 2 x 2 = 4.

So the shaded area of the petals must be 9 - 4 = 5 sq units.

Different approach, but I agree with the previously posted answer.

By the way, I wonder if even the Scholarship winners will get this! I think I was just lucky to see the solution visually quite quickly today!

WH
Minesh
Posts: 89
Joined: Sun Jul 18, 2010 9:02 pm

Re: Habs maths 2011 - question 30 can't do it

Post by Minesh »

Your name is befitting - you work hard

thank you very much for taking the trouble to look at diagram and for clear explanation
:D :)
Post Reply