2018 PSLE Discussions & Strategies (Born in 2006)

[ryka]

Iluvmygals:

While the formula for density is mass/volume, it doesn't mean that a same material will have varying density because of different volume or different mass. So, a big iron ball will have the same density as a small iron ball, even though they have different volume. The density of a material will only change when pressure or temperature changed.


So since the 3 balls existed in the same temperature and pressure, the floating ball will be a different material from the balls that sank. We don't need to know the mass and volume of the balls to conclude that they are of different density, and hence different material.

The questions showed 3 similar size balls (conclude as similar volume), the unknown / no information is the mass. Hence, there is possibility that 2 balls of the same material, one being solid and another one hollow will result in one sink (solid) and the other one floating (hollow).

[lee_yl]

@Mylilgirl,

If answer is indeed B only but current school teacher (and Sc tutor) said it’s “neither”, then I worry for our children.

Probably need to remind kids taking PSLE next year, for simple straightforward questions, don’t think too deeply into it, just move on to the next question.

[pungg]

lee_yl:

@Mylilgirl,

If answer is indeed B only but current school teacher (and Sc tutor) said it’s “neither”, then I worry for our children.

Probably need to remind kids taking PSLE next year, for simple straightforward questions, don’t think too deeply into it, just move on to the next question.

According to teacher answer is 4, 2 is wrong :roll:

[Iluvmygals]

ryka:

Iluvmygals:

While the formula for density is mass/volume, it doesn't mean that a same material will have varying density because of different volume or different mass. So, a big iron ball will have the same density as a small iron ball, even though they have different volume. The density of a material will only change when pressure or temperature changed.


So since the 3 balls existed in the same temperature and pressure, the floating ball will be a different material from the balls that sank. We don't need to know the mass and volume of the balls to conclude that they are of different density, and hence different material.

The questions showed 3 similar size balls (conclude as similar volume), the unknown / no information is the mass. Hence, there is possibility that 2 balls of the same material, one being solid and another one hollow will result in one sink (solid) and the other one floating (hollow).

I thought it was mentioned 3 solids - X, Y, Z?

[pungg]

Iluvmygals:

ryka:

[quote=\"Iluvmygals\"]While the formula for density is mass/volume, it doesn't mean that a same material will have varying density because of different volume or different mass. So, a big iron ball will have the same density as a small iron ball, even though they have different volume. The density of a material will only change when pressure or temperature changed.


So since the 3 balls existed in the same temperature and pressure, the floating ball will be a different material from the balls that sank. We don't need to know the mass and volume of the balls to conclude that they are of different density, and hence different material.

The questions showed 3 similar size balls (conclude as similar volume), the unknown / no information is the mass. Hence, there is possibility that 2 balls of the same material, one being solid and another one hollow will result in one sink (solid) and the other one floating (hollow).

I thought it was mentioned 3 solids - X, Y, Z?[/quote]Yes, according to my DS they mentioned 3 solids..

[Iluvmygals]

I suppose the mystery of the 3 balls will only be revealed next year

[janet88]

congrats! PSLE is officially over!

[lee_yl]

pungg:

According to teacher answer is 4, 2 is wrong :roll:

If by a simple thought experiment one can already prove that choice (4) is wrong, will MOE still mark choice (2) as wrong?

[mylilgirl]

pungg:

lee_yl:

@Mylilgirl,

If answer is indeed B only but current school teacher (and Sc tutor) said it’s “neither”, then I worry for our children.

Probably need to remind kids taking PSLE next year, for simple straightforward questions, don’t think too deeply into it, just move on to the next question.

According to teacher answer is 4, 2 is wrong :roll:

My DD teacher and tutor also confirmed 4 is the correct answer. Happy for her classmates who got it correct.

[mylilgirl]

lee_yl:

pungg:

According to teacher answer is 4, 2 is wrong :roll:

If by a simple thought experiment one can already prove that choice (4) is wrong, will MOE still mark choice (2) as wrong?

My DD is super don’t care now. She told me it’s ok, just 1 wrong only mah!