Q&A - PSLE Math

[Michaelia0816]

Thanks, Tianzhu!!!

[AJH]

Thank you very much, 2cor41618 - your explanations are very clear.


I nd help with these questions:

1. At first, Ashley had 550 marbles altogether. There were 3/8 as many blue marbles as yellow marbles. Later, she bought some blue marbles. For every 4 yellow marbles she had, her father gave her 25 more yellow marbles. The total number of yellow marbles then became 1 and 2/3 times that of the blue marbles. How many blue marbles did she have in the end?

For this question,my workings so far:

11u - 550 marbles
1u - 50 marbles
8u - 400 marbles

400 yellow marbles - so, Ashley's father gave her 2500 more yellow marbles.

I'm stuck here. :scratchhead:

2. There are 4 adults. Each time, 2 adults are weighed, giving a total of 6 readings, in kg as listed below:

103.5, 111, 112.5, 117, 118, 122

What is the average mass of the 4 adults?

Thank you.

[Maths Hub]

.

[tianzhu]

AJH:

1. At first, Ashley had 550 marbles altogether. There were 3/8 as many blue marbles as yellow marbles. Later, she bought some blue marbles. For every 4 yellow marbles she had, her father gave her 25 more yellow marbles. The total number of yellow marbles then became 1 and 2/3 times that of the blue marbles. How many blue marbles did she have in the end?

For this question,my workings so far:

11u - 550 marbles
1u - 50 marbles
8u - 400 marbles

400 yellow marbles - so, Ashley's father gave her 2500 more yellow marbles.

I'm stuck here. :scratchhead:

Hi

At first, Ashley had 550 marbles altogether.

11 units ------ 550
1 unit ------ 50

Blue marbles -------- 150
Yellow marbles -------- 400

For every 4 yellow marbles she had, her father gave her 25 more yellow marbles.

Hence, for 400 yellow marbles, her father gave another 2500 yellow marbles.

In the end there are 2900 yellow marbles.

The total number of yellow marbles then became 1 and 2/3 times that of the blue marbles.

5 parts ------- 2900

1 part ------- 580

3 parts ------- 1740 (blue marbles in the end)

Best wishes

[tianzhu]

AJH:

2. There are 4 adults. Each time, 2 adults are weighed, giving a total of 6 readings, in kg as listed below:

103.5, 111, 112.5, 117, 118, 122

What is the average mass of the 4 adults?

Thank you.

Hi

Let call the 4 adults, A,B,C and D.

They can be grouped as such for the weighing sessions. This’ll give us 6 readings.

AB
AC
AD

BC
BD

CD

So, you can see there are 3 groups of (A+B+C+D)

A+B+C+D ------- (103.5+111+112.5+117+118+122)/3

A+B+C+D ------- 228

Hence the average is 228/4 -------- 57

Best wishes

[dicoyote]

A group of pupils calculated their average score for a class test. They found that if one of them scored another 22 marks, their average mark would be 90. However, if one of them scored 8 marks less, their average mark would be 80. How many pupils were there in the group?


Thanks in advanced

[2cor41618]

dicoyote:

A group of pupils calculated their average score for a class test. They found that if one of them scored another 22 marks, their average mark would be 90. However, if one of them scored 8 marks less, their average mark would be 80. How many pupils were there in the group?


Thanks in advanced

Let the number of pupils be 1u.

If one of them score 22 marks more, the average is 90. This means that the total will b 90x 1u -22=90u -22.

If one of them score 8 marks less, the average will b 80. This means that the total is 80u +8.

Therefore, 90u-22=80u+8
10u=30
1u=3

Ans:3 pupils

[kiasuaunt]

Hi.


Q1.
Mr Lee sold 15% of his cupcakes on Monday.
He sold 90 fewer cupcakes on Tuesday than on Monday.
He then sold 70 fewer cupcakes on Wednesday than on Tuesday.
On Thursday,he sold 330 cupcakes and found that he had half of his original number of cupcakes left.
How many cupcakes did he sell altogether?

Q2.
There are some red and green beans in a container.
If Ahmad removes 20 red beans, the ratio of the number of red beans to the number of green beans becomes 6:5.
If Ahmad removes 10 green beans, the ratio of the number of red beans to the number of green beans becomes 4:3.
How many beans are there in the container?

Q3.
Town Lala and Town Yaya are 840 km apart.
At 8.30 am, a car left Town Lala for Town Yaya , travelling at a constant speed.
At the same time, a lorry set off from Town Yaya for Town Lala at a constant speed too. At 1.30 pm, the 2 vehicles passed each other. If the speed of the car was 24 km/h faster than the lorry, find the speed of the car.

Thank you.

[MathIzzzFun]

kiasuaunt:

Hi.


Q1.
Mr Lee sold 15% of his cupcakes on Monday.
He sold 90 fewer cupcakes on Tuesday than on Monday.
He then sold 70 fewer cupcakes on Wednesday than on Tuesday.
On Thursday,he sold 330 cupcakes and found that he had half of his original number of cupcakes left.
How many cupcakes did he sell altogether?

Q2.
There are some red and green beans in a container.
If Ahmad removes 20 red beans, the ratio of the number of red beans to the number of green beans becomes 6:5.
If Ahmad removes 10 green beans, the ratio of the number of red beans to the number of green beans becomes 4:3.
How many beans are there in the container?

Thank you.

Hi

for Q1, you may want to start with :
Total number of cakes = 100u and then work through the question to the end and equating the remainder to 50u

I will start with Mon & Tue, and hopefully you can complete the rest...

Total --> 100u

Mon-- Sold 15u, Left 85u
Tue -- Sold 15u-90, Left 70u+90

Q2.
If Ahmad removes 20 red beans, the ratio of the number of red beans to the number of green beans becomes 6:5
So, total number of beans in container,
Red beans : Green beans --> 6u + 20 : 5u -- total --> 11u + 20

If If Ahmad removes 10 green beans, the ratio of the number of red beans to the number of green beans becomes 4:3:

Red beans : Green beans --> 6u+20 : 5u-10 = 4:3
cross-multiply/equalize:
18u+60=20u-40
1u--> 50

Total number of beans --> 11 x 50 + 20 = 570

cheers.

[MathIzzzFun]

kiasuaunt:

Hi.


Q1.
Mr Lee sold 15% of his cupcakes on Monday.
He sold 90 fewer cupcakes on Tuesday than on Monday.
He then sold 70 fewer cupcakes on Wednesday than on Tuesday.
On Thursday,he sold 330 cupcakes and found that he had half of his original number of cupcakes left.
How many cupcakes did he sell altogether?

Q2.
There are some red and green beans in a container.
If Ahmad removes 20 red beans, the ratio of the number of red beans to the number of green beans becomes 6:5.
If Ahmad removes 10 green beans, the ratio of the number of red beans to the number of green beans becomes 4:3.
How many beans are there in the container?

Q3.
Town Lala and Town Yaya are 840 km apart.
At 8.30 am, a car left Town Lala for Town Yaya , travelling at a constant speed.
At the same time, a lorry set off from Town Yaya for Town Lala at a constant speed too. At 1.30 pm, the 2 vehicles passed each other. If the speed of the car was 24 km/h faster than the lorry, find the speed of the car.

Thank you.

Hi
Q3.
8.30am to 1.30pm --> 5h
5h x 24 km/h --> 120 km
when the car and the lorry passed each other, the car travelled 120 km more than the lorry.

Total distance --> 840 km, car travelled 120 km more than the lorry -- can you continue from here ? ie sum of two numbers = 840, difference of the numbers = 120.

cheers.