Q&A - PSLE Math

[SOS mum]

Hi all, ps help. Many tks and God Bless:)

(1) James used 4/7 of his screws and 3/5 of his nails to construct a wooden cupboard. In the end, he had an equal number of screws and nails left. Given that James had a total of 145 screws and nails at first, how many nails did he use to construct the wooden cupboard?

(2) At a fun-raising event, 60% of the people were male and the rest were female. 20% of the female left the event in the afternoon. In the evening, after 33 male and 35 female left the event, 75% of the people at the event were male.
(a) What percentage of the people left the event in the afternoon?
(b) How many people were there at the start of the fun raising event?

[Ender]

Someone help me for this question please.

The Robotics Club had twice as many pupils as the Science Club. The ratio of the number of girls to the number of boys in the Robotics Club was 4:1. The ratio of the number of girls to the number of boys in the Science Club was 2:3.
(a) Find the ratio of the number of girls in the Robotics Club to the number of girls in the Science Club.
(b) After 38 girls left the Robotics Club to join the Science Club, the ratio of the number of girls to the number of boys in the Science Club became 9:4. How many girls were in the Science Club in the end?

Science Club

Code: Select all

G : B : Total
2 : 3 : 5

Robotic Club

Code: Select all

G : B : Total
4 : 1 :  5

Since we know the total of the Robotic is twice that of the Science CLub, we can make both of the club share a common unit for the ratio.
In this case we multiply a factor of 2 to Robotic club to make the total twice of Science Club

Below we have all the ratio sharing a common unit 'u', by making the total of robotic club 10u, which is twice of Science Club of 5u.

Code: Select all

Robotic Club    Science Club
G : B : Total    G : B :Total
8 : 2 : 10       2 : 3 : 5

a) Ratio of girls in robotic club to the girls in Science club is 8 : 2 => 4 : 1 ####

b) For the Science Club,
Before increase of girls, G : B => 2 : 3

After increase on girls, G : B => 9 : 4

What is constant here is the number of boys is the same. We'll make the ratio common for the boys
Before increase of girls, G : B => 8 : 12 (Multiple by 4)
After increase of girls, G : B => 27 : 12 (Mulitple by 3)

Increase in girls 27u-8u = 38
19u = 38
u = 2

In the end, the girls in Science Club = 27u = 54 ####

[Ender]

Hi all, ps help. Many tks and God Bless:)

(1) James used 4/7 of his screws and 3/5 of his nails to construct a wooden cupboard. In the end, he had an equal number of screws and nails left. Given that James had a total of 145 screws and nails at first, how many nails did he use to construct the wooden cupboard?

Code: Select all

Screws           Nails
Used : Unuse    Used : Unuse
4    :  3         3  :  2

Since he has equal number of leftover screws and nails, we can get common unit by making them the same ratio.

Code: Select all

Screws (x 2)       Nails (x 3)
Used : Unuse    Used : Unuse
8    :  6         9  :  6

Total Screws = 8u + 6u = 14u
Total Nails = 9u + 6u = 15u

14u+15u = 145
29u = 145
u = 5

Nails used = 9u = 45 ##

[Ender]

Hi all, ps help. Many tks and God Bless:)
(2) At a fun-raising event, 60% of the people were male and the rest were female. 20% of the female left the event in the afternoon. In the evening, after 33 male and 35 female left the event, 75% of the people at the event were male.
(a) What percentage of the people left the event in the afternoon?
(b) How many people were there at the start of the fun raising event?

At the start, let the total of male and female = 100u

Code: Select all

Male: Female
60u : 40u

20% of 40u of female left the party = 8u

a) % of people left = 8u/100u X 100 = 8% ###

b)

Code: Select all

Male : Female
60u  : 32u
-33    -35
75p  : 25p

60u - 33 = 75p
32u - 35 = 25p
96u - 105 = 75p

96u - 105 = 60u -33
36u = 72
u = 2

At the start there are 100u = 200 people ###

[sushi88]

Someone help me for this question please.

The Robotics Club had twice as many pupils as the Science Club. The ratio of the number of girls to the number of boys in the Robotics Club was 4:1. The ratio of the number of girls to the number of boys in the Science Club was 2:3.
(a) Find the ratio of the number of girls in the Robotics Club to the number of girls in the Science Club.
(b) After 38 girls left the Robotics Club to join the Science Club, the ratio of the number of girls to the number of boys in the Science Club became 9:4. How many girls were in the Science Club in the end?

Club--------------G----------B
R-club initial-----8u---------2u (4:1)
S-club initial-----2u---------3u
After rec 38, S--2u+38-----3u
New ratio for S---9----------4

(a) Ratio of R-girls : S-girls is 8u : 2u = 4: 1

(b) (2u+38)/3u -> 9/4
8u + 152 -> 27u
19u -> 152
u->8
Hence girls in S club in the end is 2(8)+38 = 54

[Jmaths.SG]

Hi all, ps help. Many tks and God Bless:)

(1) James used 4/7 of his screws and 3/5 of his nails to construct a wooden cupboard. In the end, he had an equal number of screws and nails left. Given that James had a total of 145 screws and nails at first, how many nails did he use to construct the wooden cupboard?

Solution with video in the following link:
https://www.facebook.com/permalink.php? ... 4939707325

[happy to be mum]

need help..

A circular wheel of diameter 35cm makes 100 revolutions in 1 minute. Calculate the distance covered by the wheel in half an hour. Express your answer in km.

[MathWithModels]

Question:

A circular wheel of diameter 35cm makes 100 revolutions in 1 minute.
Calculate the distance covered by the wheel in half an hour. Express your answer in km.

Answer:

Radius of the wheel: 35 / 2 = 17.5 cm
Circumference of the wheel: 2 x Pi x Radius = 2 x 3.14 x 17.5 cm = 109.9 cm
Distance covered by the wheel in 1 minute = 109.9 x 100 = 10990 cm
Distance covered by the wheel in half an hour = 10990 x 30 = 329700 cm = 3.297 km

Thanks, Ender, for pointing out the mistake. Fixed now.

[SOS mum]

Thank you very much, Ender

[SOS mum]

Hi all, ps help. Many tks and God Bless:)
(2) At a fun-raising event, 60% of the people were male and the rest were female. 20% of the female left the event in the afternoon. In the evening, after 33 male and 35 female left the event, 75% of the people at the event were male.
(a) What percentage of the people left the event in the afternoon?
(b) How many people were there at the start of the fun raising event?

At the start, let the total of male and female = 100u

Code: Select all

Male: Female
60u : 40u

20% of 40u of female left the party = 8u

a) % of people left = 8u/100u X 100 = 8% ###

b)

Code: Select all

Male : Female


60u  : 32u
-33    -35
75p  : 25p

60u - 33 = 75p
32u - 35 = 25p
96u - 105 = 75p

96u - 105 = 60u -33
36u = 72
u = 2

At the start there are 100u = 200 people ###

Thank you very much, Ender