A primary 6 maths problem help.

• Chunghong2004

  9 Aug 08, 11:42

  Can some help me with this?

   

  Given the perimeter of a semicricle is 61.68, find the diameter of the circle taking that pie=3.14

   

  thanks.

• Uncertain

  9 Aug 08, 11:48

  (0.5)(3.14)d + d = 61.68

  LHS: test student alegbra <-- they should know what to do

  Then divide to find "d". This is still within primary school student capability

• MyPillowTalks

  9 Aug 08, 12:13

  Circumference of semicircle = 1/2 x pi x D

  Perimeter of semicircle = 1/2 x pi x D + D

  Given perimeter of semicircle = 61.68, we can say:

  1/2 x pi x D + D = 61.68

  1/2 x 3.14 x D + D =61.68

  1.57D+D= 61.68

  D x (1.57+1)= 61.68

  D x 2.57= 61.68

  D = 61.68/2.57

  D= 24

  To check,

  Sub D = 24 into 1/2 x 3.14 x D +D

  1/2 x 3.14 x 24 + 24

  Perimeter:

   1.57 x 24 + 24

   37.68 + 24

  = 61.68

   

  CORRECT!

   

• MyPillowTalks

  9 Aug 08, 12:13

  double

• Maith

  10 Aug 08, 00:50

  walao,pri 6 got this alr ar?

• a-Lost-9uY

  10 Aug 08, 01:00

  39.286?

• bonkysleuth

  10 Aug 08, 11:51

  Originally posted by Maith:

  walao,pri 6 got this alr ar?

  
  i remember vividly learning this when i was in primary 6.

• maurizio13

  10 Aug 08, 12:04

  Perimeter of Semi-circle = 61.68

  Circumference of Circle = 2(61.68 - 2R)

  **Because the perimeter includes the diameter of the semi-circle (2 x R)

   

  2(pi)R = 2(61.68 - 2R)

  3.14R = 61.68 - 2R

  5.14R = 61.68

  R = 12

   

  Therefore diameter of circle is twice of radius, which means D = 2 x 12 = 24

   

• Chunghong2004

  10 Aug 08, 20:18

  thank you everyone for your help.