Pri 6 maths questions

• skythewood

  5 Oct 08, 15:04

  Originally posted by technoboy:

  3) P overlaps Q & R. Q is on R. Ratio of area of P, Q, R is 1:2:3. 40% of Q is shaded.Find the % of the figure unshaded.

  

  P: Q : R

  1 : 2  : 3

  unshaded R = 3units - 2units
                       = 1units

  since 40% of Q is shaded, 80% of P is shaded. since ratio of P:Q is 1:2

  unshaded P = 20%/100 x 1 unit
                        =  1/5 unit

  unshaded Q = 60%/100 x 2 units
                        = 6/5 units

  shaded Q = 40%/100 x 2 units
                     = 4/5 unit

  total unshaded = 1 unit + 1/5 unit + 6/5 unit
                            = 2 and 2/5 unit

  total area = 2 and 2/5 units + 4/5 units
                    =  3 and 1/5 units

  percentage = 12/5 units divide by 16/5 units
                      = 75%

• technoboy

  5 Oct 08, 17:19

  Originally posted by skythewood:

  presently,

  $50 ===>   X X X
  $10 ===>   X X X X X X X X

  at the beginning, before taking away 3/4 of $50

  $50 ===> X X X X X X X X X X X X 
  $10 ===> X X X X X X X X
  number of notes is 151 + 9 = 160  (include the 9 $10)

  simplify diagram to

  $50 ===> X X X
  $10 ===> X X

  one X is equal to 160/5 = 32 notes

  hence, you can solve the thing

   

   

  Got this! Thanks alot!

• technoboy

  5 Oct 08, 17:21

  Originally posted by skythewood:

  a) speed = distance divide by time
                  = 1500 / 150
                  =  10m/s

  b) the 100 seconds is the time between the end of the train get on the bridge, and the front of the train reach the end of the train.

  distance travelled  = speed x time
                                  = 10 x 100
                                  - 1000m

  hence, the train is = 1500 - 1000
                                 = 500m

   

     bridge starts   |< ------------------1500------------------------------------>| bridge ends
                                                           
                              | train starts|<------------distance travelled---------->|
  
                                                                                             | train ends |

  Hmm, this answer isn't correct leh. Answer is 12m/s for the speed of train and 300m for the length of train. Any ideas how?

• technoboy

  5 Oct 08, 17:21

  Originally posted by skythewood:

  P: Q : R

  1 : 2  : 3

  unshaded R = 3units - 2units
                       = 1units

  Can you explain this very first step? Don't quite get it. Thanks once again!

• skythewood

  5 Oct 08, 17:26

  Originally posted by technoboy:

  Can you explain this very first step? Don't quite get it. Thanks once again!

  You see Q and R in the picture?

  Q is inside R. the ratio of Q:R is 2:3

  the area of R that is not covered by Q is = 3units(R) - 2 unit(Q)

                                                                       = 1 unit

• skythewood

  5 Oct 08, 17:35

  Originally posted by technoboy:

  2) The length of a bridge is 1500m. A train takes 150secs to travel on the bridge. The whole train was completely on the bridge for 100secs. Find (a) the average speed of the train and (b) the length of the train

  if the answer is 12m/s, than the 150 sec to travel on the bridge means the time starts when the train gets on bridge, and stops when train get off bridge.

  i interpreted it as it take 150s to travel the 1500m of the bridge. sorry, my bad.

  for 150 seconds, the train travel 1500m + length of train

  for 100 seconds, the train travel 1500m - length of train

  so in 50 seconds, the train travel twice the length of train

  in 25 seconds, the train travel the length of the train.

  in 125 seconds, the train travel the 1500m.

   

  if you follow my train of thoughts, you can solve this le. 

   

• technoboy

  5 Oct 08, 17:36

  Oh ok understood. Initially thought the unshaded R is inclusive of the unshaded Q area.