Q&A - PSLE Math

[MathIzzzFun]

jarenchuatw:

Thanks Master MathizzzFun.


Got one more question that is making my head crack....

Motorcyclist A and B started a 360km race. They rode their bikes at the same speed for the first 120km. For the rest of the 240km, A rode at a faster speed. He arrive at the finishing point 1omins before B who was 40 km behind him. B did not chang his speed for the whole race. B completed the rae at 3.10pm

a) At what time did they start the race?
b) What was A's average speed for the last 240 km in m/min?

hi

..me not Master la... just helping around here..

A reached the finishing point 10 min before B and B is 40 km behind
--> B will take 10 min to cover 40 km, ie B's speed = 40 km/10 min = 240 km/h
Total time taken for the 360 km = 360/240 h = 1.5 h = 1h 30 min
1h 30 min before 3.10pm --> 1.40 pm
They started the race at 1.40pm

For the last 240 km, when A covered 240 km, B covered only 200 km
So, A's speed = 240/200 x 240 km/h = 288 km/h

cheers.

[jarenchuatw]

Thanks MathIzzzFun for the prompt reply.


However, I could not quite understand part (b)…is there another way to explain it?

[MathIzzzFun]

jarenchuatw:

Thanks MathIzzzFun for the prompt reply.


However, I could not quite understand part (b)...is there another way to explain it?

Hi

for the last 240 km, time taken by B = 240/240 = 1h
Time taken by A = 1h - 10min = 50 min
A's speed = 240 km/50 min = 288 km/h

cheers.

[jarenchuatw]

MathsIzzzFun…wow, that’s so much clearer…million tks again!

[Essential]

Hi please help my DS for question 14 . John shifted the decimal point of a number twice to the left to obtain a new number . The difference between the new number and the original number was 136.62. A) how many times of the new number is the original number ? B) what is the sum of the 2 numbers ?

[MathIzzzFun]

Essential:

Hi please help my DS for question 14 . John shifted the decimal point of a number twice to the left to obtain a new number . The difference between the new number and the original number was 136.62. A) how many times of the new number is the original number ? B) what is the sum of the 2 numbers ?

Hi

decimal point shifted twice to the left = dividing by 100
so, new number is 1/100 of original number.
Difference = 99/100 of original number
original number = 136.62/99 x 100 = 138
.. with this, part b should be a breeze

cheers.

[tianzhu]

Essential:

Hi please help my DS for question 14 . John shifted the decimal point of a number twice to the left to obtain a new number . The difference between the new number and the original number was 136.62. A) how many times of the new number is the original number ? B) what is the sum of the 2 numbers ?

Hi

Original number ----- 100 units

New number ------ 1 unit

100 – 1 ----- 99

99 units ------- 136.62

1 unit ----- 1.38

Original number ----- 100 units ------- 138

New number ------ 1 unit ------ 1.38

The original number is 100 times the new number.

Sum of 2 numbers ------ 101 units ------- 139.38 (138 + 1.38)

Best wishes

[Winx5015]

Hi, need help for the following questions.


(1) If Ahmad and Ben work together, they can complete a job in 8 days. If Ahmad were to work alone for 2 days, he can finish 3/20 of the job in 2 days. How many days will Ben take to complete the job if he were to work alone?

(2) Steve and Huiling took part in a walkathon which started at 6.30am. Steve's average speed was 15 m/min faster than Huiling. Both of them did not change their speed throughout the walkathon. When Steve reached the finishing line after 40 minutes, Huiling had only walked 8/9 of the distance.
(a) What time was it when Huiling completed the walkathon?
(b) Find Steve's average speed for the walkathon in m/min.

(3) At a concert, tickets were sold at $12, $30 and $50. The sales of $12 tickets made up 25% of the total amount of money collected. The sales of $30 tickets made up 60% of the total amount. given that 5 more $12 tickets were sold than the $30 tickets, how many $50 tickets were sold?

(4) At a funfair, the children can choose to ride on the Merry-Go-Round of the Train or both with their coupons. 7/10 of the children chose the Merry-Go-round, 45% chose to ride on the Train, and 10% of the children did not take any of the two rides. A total of 75 children went for both rides.
(a) How many children took ONE ride at the Merry-Go-Round only?
(b) How many children did not take any rides?

Thanks:)

[MathIzzzFun]

Winx5015:

Hi, need help for the following questions.


(1) If Ahmad and Ben work together, they can complete a job in 8 days. If Ahmad were to work alone for 2 days, he can finish 3/20 of the job in 2 days. How many days will Ben take to complete the job if he were to work alone?

Thanks:)

Q1.

Ahmad & Ben --> 8 days ---> 20 units of work
Ahmad --> 2 days --> 3 units of work
Ahmad --> 8 days --> 12 units of work
Ben --> 8 days --> (20-12) = 8 units of work
Ben --> 20 units of work --> 20 days
Ben will take 20 days to complete the work on his own.

cheers.

[MathIzzzFun]

Winx5015:

Hi, need help for the following questions.


(2) Steve and Huiling took part in a walkathon which started at 6.30am. Steve's average speed was 15 m/min faster than Huiling. Both of them did not change their speed throughout the walkathon. When Steve reached the finishing line after 40 minutes, Huiling had only walked 8/9 of the distance.
(a) What time was it when Huiling completed the walkathon?
(b) Find Steve's average speed for the walkathon in m/min.

Thanks:)

Q2.

when Steve reached finishing line,
distance covered by Steve : Huiling --> 9 : 8
time ratio, Steve : Huiling --> 8:9
Time taken by Huiling to reach finish line = 9/8 x 40 min = 45 min
6.30 am + 45 min --> 7.15 am
Huiling reached the finish line at 7.15 am

Steve's speed: Huiling's speed = 9 : 8
Steve's speed = 9 x 15 m/min = 135 m/min

cheers.