Q&A - PSLE Math

[zanen]

can help too? 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?

[MathIzzzFun]

jewelbox:

MathIzzzFun, thanks for the soln on vol of water in tank with tap A and B. I dont understand why must 'assuming tap A fill tank in last 3 min' and the steps after it.


Why cant i do :
Since it takes 6min to fill 0.9cm, it takes 500min to fill 75cm. Thus ans is 500min.
Thanks.

this is a typical \"slipping snail question ie a snail climbs a wall and slips\"

We cannot use 0.9cm/6 min as a uniform rate to calculate because it is actually filling up 1.5 cm over 3 min and then draining 0.6 cm over another 3 min.
So, it takes 6 min to fill 0.9 cm PROVIDED, the remaining height is more than 1.5cm because in 3 min, Tap A will fill up 1.5cm and the water level only starts to fall after tap B is turned on.

If the remaining height to fill is only 1 cm, then we will see that tap A will fill up 1 cm in 2 min.

Therefore, we need to consider the final lap ie assuming tap A filling up the tank to full in the final 3 min.

Otherwise, one can work out multiple of 0.9 cm such that the difference between the multiple and 75cm is less than or equal to 1.5cm, so that the remaining height can be fully filled by tap A.

cheers.

[cimman]

dicoyote:

Hi,


Need help on these question:

1) Chris and Diane have some carnival tickets. If Chris sells 10 tickets per day and Diane sells 5 tickets per day. Chris will have 40 tickets left when Diane has sold all her tickets. If Chris sells 5 tickets per day and Diane sells 10 tickets per day, Chris will have 70 tickets left when Diane has sold all her tickets.
a) How many tickets does Chris have?
b) If each ticket is sold for $20, how much money can be collected from the sale of all their tickets?

For (a), I am trying to use algebra, but could not figure out after having the days as \"x\"

10x+40=5x
5x+70=10x.....is this correct?

in Double If questions, there are 2 scenarios. For the first scenario, you can use 'a' to represent the number of days. I try not to use x as it looks like a multiplication sign. For the second scenario, you can use 'b' to represent the number of days. The number of days are different in both cases. You'll have 2 equations:
40 + 10a = 70 + 5b
5a = 10b
Chris will have (40 + 10a) tickets or (70 +5b) tickets. Both will give you the same values.

[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.

[MathIzzzFun]

zanen:

can help too? 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?

French --> 28 students
French and Maths --> 12 students
Maths only --> 48 - 28 = 20 students
French only --> 28 - 12 = 16 students
Maths --> 20 + 12 = 32 students


cheers.

[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.