Maths Homework - could someone please help with finding area and perimeter of odd shapes

(13 Posts)
yohoohoo Sun 30-Oct-16 17:30:23

DD having a meltdown with this homework on area and perimeter. Really struggling to do this

StealthPolarBear Sun 30-Oct-16 17:31:53

Well the circle - calc the area as if it's a proper circle then multiply by 0.75

StealthPolarBear Sun 30-Oct-16 17:32:42

Same for perimeter - calc as normal, remove one quarter and then add the two square sides

PumpkinsOnTheMantlepiece Sun 30-Oct-16 17:32:56

Find the perimeter of the circle using formula.
Divide by four.
Minus one part.
Add on ten ( the straight bits)

2.calculate rectangle.
Minus one end
Calculate cycle and half.
Add half and rectangle.

wanderings Sun 30-Oct-16 17:33:58

Circle picture:

Radius is 5cm. Area of whole circle is pi times radius squared. Multiply this by 3/4 or 0.75 to get area.

Perimeter: perimeter of whole circle is 2 times pi times radius. Multiply this by 3/4 or 0.75. You must also add 5cm twice, because the two straight lines are part of the perimeter.

StealthPolarBear Sun 30-Oct-16 17:34:01

The other can be calc as if it's a rectangle, having removed the 3cm radius semi circle first, and then add on the semi circle

My2centsworth Sun 30-Oct-16 17:34:56

If it is to scale you could get your DD a piece of string to measure the perimeter with a ruler and that might help her understand a bit better.

LIZS Sun 30-Oct-16 17:35:24

Area of shape one is , assuming the chunk taken out 90o angle at centre , 3/4 of the area of the circle. likewise perimeter will be 3/4 of the circumference + the 5cm radius x 2

The second one will be the area of the rectangle plus area of semi circle , perimeter is 2 long sidesof rectangle + one short and half the circumference of the circle.

StealthPolarBear Sun 30-Oct-16 17:35:37

So a rectangle of 22 x 9 and a 3cm semi circle

wanderings Sun 30-Oct-16 17:39:53

Radius of semicircle in the rectangle question is not 3cm; it is 4.5cm.

StealthPolarBear Sun 30-Oct-16 18:00:14

Of course sorry

irvineoneohone Sun 30-Oct-16 19:20:58

I was talking about these today with my ds.
I think you need to be able to see
1) whole circle - 1/4 of circle.
2) rectangle + semi circle.

Once you get a hang of it it will get easy, if you know the formula for calculating areas of different shapes.

CookieDoughKid Sat 05-Nov-16 12:29:48

I think it would help to check your son's basics are secure like fractions and individual shaped area calculations like just circle and just square. Find half a square. Find 3/4 a square. Ensure he understands decimal equivalent of fractions. Once all the basic elements are secure this would be much easier for him. I would definitely check for gaps in his maths first.

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