MAths F.1(30 FUN)

2. average typing speed = total words / total time

the time used for typing 1000 words at a speed of 30 words/min:
speed = words/ time
time = words /speed
= 1000/30
= 100/3 mins

the time used used for typing 750 words at a speed of 40 words/min:
time = words /speed
= 750/40
= 75/4 mins

the average typing speed
= total words / total time
= (1000 + 750 ) / (100/3 + 75/4)
= 33.6 words / min

therefore, her average typing speed = 33.6 words/ min


3.
(a) average speed = total distance of journey / total time
total distance of journey
= average speed x total time
= 600 x 10
= 6000m

the distance travelled by joe in the last 1/3 of his journey = 6000 x 1/3 = 2000m
his speed in the last 1/3 of his journey was 500m/min
speed = distance /time
500 = 2000 /time
time = 4

therefore he took 4 mins in the last 1/3 of his journey.

(B)
Joe took 4 mins to travel 2000m in the last 1/3 of journey
the remainning distance = 6000 - 2000 = 4000 m
the remaining time = 10 - 4 = 6 mins

his speed in the remaining journey
= distance / time
= (6000 - 2000) / (10 - 4)
= 2000 / 3
= 666.67 (correct to 2 decimal spaces)

therefore, his speed in the remaining journey is 666.67m/min

第二題..
假設佢打左1750 個字(分別用唔通speed 黎打)
咁我計左佢打1750 個字用左幾多分鐘先啦..

1000/30 + 750/40 = 625/12 minutes

咁佢total 打左1750 個字喎.. 咁計佢ge speed 就係︰

1750 / (625/12) = 33.6 words/min 喇

第三題..
a) total distance of the journey = 600/10=6000m
1/3 of the journey = 6000/3=2000m
time taken for the 1/3 of the journey = 2000/500=4 min
b) time taken for the 2/3 of the journey = 10-4 = 6 min
distance for the 2/3 of the journey = 6000-2000=4000m
speed for this 2/3 of the journey = 4000/6=666.666666667 m/min

唔知有冇計錯..