Q&A - PSLE Math

[MathIzzzFun]

tech_nomax:

Please help with the following questions:


2) Two buses X and Y left ABC interchange at 6.35 a.m. to pick up passengers. They travelled at an uniform speed in opposite directions round a 55 km circular route. Bus X took 50 minutes to complete each round. After every 30 minutes, the two buses would meet. At what time would the two buses meet at the interchange again?

Thank you.

2) lowest common multiple of 30 & 50 = 150
6.35 a.m. + 150 min --> 9.05 a.m.
The two buses will meet again at the interchange at 9.05 a.m.

cheers.

[Muffins]

\"In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?\"


Hi

If 7/12 of the students chose French and 1/4 chose both Maths and French, then the remainder chose mathematics. So the remainder of people = 1 - (7/12 + 1/4) = 1 - 5/6 = 1/6

So, if 1/6 chose only Maths, then the number of students who chose it is (48 x 1/6) = 8 students

Cheers!

[jewelbox]

MathIzzzFun,

thanks for your explanation on vol. Now that i understand tt it is ‘snail up and down’ type qn, it helps in digesting the soln.

Also, appreciate your explanation to the qn on triangle on 19sep on why angle DEC is 3 units and so on. Thanks v much.

[MathIzzzFun]

Muffins:

\"In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?\"


Hi

If 7/12 of the students chose French and 1/4 chose both Maths and French, then the remainder chose mathematics. So the remainder of people = 1 - (7/12 + 1/4) = 1 - 5/6 = 1/6

So, if 1/6 chose only Maths, then the number of students who chose it is (48 x 1/6) = 8 students

Cheers!

note that the number of students taking French refers to students who take ONLY French and students who take both French and maths.

hope this diagram help...


http://i50.tinypic.com/2eow61i.png\">

cheers.

[MathIzzzFun]

jewelbox:

MathIzzzFun,

thanks for your explanation on vol. Now that i understand tt it is 'snail up and down' type qn, it helps in digesting the soln.

Also, appreciate your explanation to the qn on triangle on 19sep on why angle DEC is 3 units and so on. Thanks v much.

hope this helps..


http://i47.tinypic.com/10nvr7b.png\">

cheers.

[kwcllf]

MathIzzzFun:

zanen:

someone pls help Mr Tan drives from Town A to Town B, a distance of 720 km,at a constant speed. When he returns from Town B to Town A, he saves an hour of travel time by increasing his average speed by 10 km/h. Find the total time taken for the whole journey (to and fro).

720 km = 80 km/h x 9 h = 90 km/h x 8h
total time = 8h+9h =17h

cheers.

Hi sorry to bother.

Is there a more detailed or alternative explanation so that my DS can understand better?

Thanks

[tianzhu]

kwcllf:

Is there a more detailed or alternative explanation so that my DS can understand better?

Hi

This question is crafted in such a way that it’s pretty neat to use “Guess and Check” strategy.

Use it with logical reasoning. What are the usual speeds of cars travelling from point A to point B?

Plug the numbers in and you should be able to come up with a speed of 80km/h and 90km/h and a time difference of 1h.

Do not forget about “GC”, it might help us to gain some marks.

Another way is to use algebra if a child is well versed in it.

Best wishes

[fantasy1]

Hi


Can anyone help me with these 2 problems?

1)Last month,MAy spent 1/4 of her income on transport, 45% on food and saved the rest.
Her income was increased by 1/10 in this month.
Spent the same amount on transport but increased her savings by 30%.
She saved $780 this month.
(a) How much did she spend on food this month?


2)7 apples cost as much as 2 mongoes. 5 oranges cost as much as a mango.
Find the ratio of the cost of one applke to the cost of one mango to the cost of one orange.



Thank You

[fantasy1]

Hi


Can anyone help to solve these 2 maths problems?

1)Last month May spent 1/4 of her income on transport, 45% on food and saved the rest.
Her income was increased by 1/10 in this month.
She spent the same amount on transport but increased her savings by 30%.
She saved $780 this month.
(a) how much did she spend on food this month?

2)7 apples cost as much as 2 mangoes. 5 oranges cost as much as a mango. Find the ratio of the cost of one appl to the cost of one mango to the cost of one orange.


Thanbk You

[tianzhu]

fantasy1:

Hi


Can anyone help me with these 2 problems?

1)Last month,MAy spent 1/4 of her income on transport, 45% on food and saved the rest.
Her income was increased by 1/10 in this month.
Spent the same amount on transport but increased her savings by 30%.
She saved $780 this month.
(a) How much did she spend on food this month?


2)7 apples cost as much as 2 mongoes. 5 oranges cost as much as a mango.
Find the ratio of the cost of one applke to the cost of one mango to the cost of one orange.

Hi

1)

A neat way is to use MD.

Consider the savings this month.

13u ------ 780

10u ------- 600 (last month’s savings)

Last month

25% ------- transport

45% ------- food

30% -------- food

30% -------- 600

10% ------- 200

Income last month ------- 100% ------- 2000

Income this month ------- 2200

Transport ------- 500 (same amount)

Savings ------- 780

Food’s spending ------- 2200 – 500-780 ------- 920

2)

Use 70 units for the cost.

1 apple ------- 10 units

1 mango ------ 35 units

1 orange -------- 7 units

A : M: 0 ------- 10:35:7

Best wishes