Q&A - PSLE Math

[tianzhu]

Michaelia0816:

3) Mary is 5 years older than Alice. In 3 years' time, Mary will be twice as old as Alice. How old will Mary be in 10 years' time.

Hi

Again, rely on the key point “Age difference stays the same”.

I believe the best way is to let you try out the question yourself.

Here are some pointers; you need to find their present ages first (Alice --- 2 and Mary --- 7)

The answer is 17.

Best wishes

[Michaelia0816]

Ok , I almost needed to use GC, But my teacher told me in class yesterday that got a heuristic way!

[Michaelia0816]

Thx Tianzhu!

[Michaelia0816]

For my Q2, my statement is the same bit I did not stop at 14,I times it, my big mistake!

[Michaelia0816]

tianzhu:

Hi girl


I’ll further elaborate on my earlier solution.Hope this helps.

At the beginning of the party we have 160 boys and 100 girls. This gives a difference of 60 more boys.

In the end, the number of boys at the party became thrice the number of girls.

Boys:Girls ------- 3:1

Since an equal number of boys and girls left the party, the difference in the number of boys and girls remains the same before and after.

2u-------60
1u-------30

Number of girls who left the party ------ 100 - 30 ------ 70

Best wishes

PS ----- It’s important to understand the concept and be able to apply to similar types of questions during examinations. Try going through the solution again and if it bothers you, let me know which areas tripped you. I’ll try to see if I can make it clearer.


Flow of events

Number of boys@first ------- 160
Number of girls@first ------- 100
Difference@first ------- 60

Number of boys@left the party ------- 70
Number of girls@left the party ------- 70

Number of boys@end------- 90 (160-70)
Number of girls@end ------- 30 (100-70)
Difference@first ------- 60

Why must be divided by 2? I tried to divide it but cannot get the answer, I was struck at this statement at my HW.

[tianzhu]

Michaelia0816:

Why must be divided by 2? I tried to divide it but cannot get the answer, I was struck at this statement at my HW.

Hi

In the end, the number of boys at the party became thrice the number of girls.

Boys:Girls ------- 3:1

In MD format, we’ll have 3 boxes to show the number of boys and 1 box to show the number of girls.

The difference is 2 boxes or units.

2 units ------ 60

1 unit ------ 30

Best wishes

[Michaelia0816]

Ok, I get the answer already, Thanks!

[tianzhu]

Michaelia0816:

For my Q2, my statement is the same bit I did not stop at 14,I times it, my big mistake!

Hi

The brutal truth is that mistakes would be made now and then.

It’s better to make it now in this forum and learn from it rather than the actual PSLE exam.

You’re a bright young girl; you should be able to tackle the challenges ahead of you.

Best wishes

[Michaelia0816]

Thx

[tianzhu]

Michaelia0816:

Ok , I almost needed to use GC, But my teacher told me in class yesterday that got a heuristic way!

Hi girl

Do not forget that GC is also one of the heuristics in primary maths syllabus.

Best wishes