Q&A - PSLE Math

[smileplease]

Anyone knows how to do this Q :


There were 1960 workers in a garment factory this year. This is 840 less than that of last year. Find the percentage decrease in the number of workers?

How do we determine it is 840/2800 x 100 OR 840/1960 x 100?

thanks.

[MathIzzzFun]

maths6a:

Hi need help with this qn.

Has anyone posted it yet? pl direct me to the page. Thanks.

A, B and C were standing in a straight line waiting for a race to start.
C was 300 m ahead of B and B was 100 m ahead of A. At 9 am, they started the race. A overtook B in 5 min. In another 5 min, A overtook C. If B's speed is 150 m/min, at what time did B overtake C?

Thanks in advance.

Hi

A made up 100m to catch up with B in 5 min.
100m/5 min = 20 m/min, so A is 20 m/min faster than B, ie A's speed = 170 m/min

A made up 400 m to catch up with C in 10 min.
400m/10min = 40m/min, A's is 40m/min faster than C.
C's speed = 170m/min - 40m/min = 130m/min

150m/min - 130/min = 20 m/min - B is 20 m/min faster than C
300m / 20m/min = 15 min
B will overtake C 15 min later, at 9.15am

cheers.

[maths6a]

Correct me if I am wrong, but

840/2800 x 100% is the correct answer because percentage decrease is compared to what was at first/original which in this case was last year.

[atutor2001]

smileplease:

Anyone knows how to do this Q :


There were 1960 workers in a garment factory this year. This is 840 less than that of last year. Find the percentage decrease in the number of workers?

How do we determine it is 840/2800 x 100 OR 840/1960 x 100?

thanks.

This one I know.
Decrease is changing from BIG to small so the original/start is BIG -> divide by BIG
Increase is changing from SMALL to big so the original/start is SMALL -> divide by SMALL
That was how I told my kids in those good old days.

[ck123]

Hi smileplease


It is 840/2800 X 100

[MathIzzzFun]

smileplease:

Anyone knows how to do this Q :


There were 1960 workers in a garment factory this year. This is 840 less than that of last year. Find the percentage decrease in the number of workers?

How do we determine it is 840/2800 x 100 OR 840/1960 x 100?

thanks.

Hi

the question is asking for percentage decrease which means that the reference point is last year.

Number of workers last year = 1960 + 840 = 2800

so, percentage decrease = 840/2800 x 100%

cheers.

[smileplease]

atutor2001:

smileplease:

Anyone knows how to do this Q :


There were 1960 workers in a garment factory this year. This is 840 less than that of last year. Find the percentage decrease in the number of workers?

How do we determine it is 840/2800 x 100 OR 840/1960 x 100?

thanks.

This one I know.
Decrease is changing from BIG to small so the original/start is BIG -> divide by BIG
Increase is changing from SMALL to big so the original/start is SMALL -> divide by SMALL
That was how I told my kids in those good old days.

:thankyou:

[smileplease]

Need help on this Q:


Ginny had two boxes of greeting cards. After she had transferred 1/5 of the greeting cards in box A to box B, the ratio of the number of greeting cards in box A to the number of greeting cards in box B is 3:5. What was the ratio of the number of greeting cards in box A to the number of greeting cards in box B at first?

[MathIzzzFun]

smileplease:

Need help on this Q:


Ginny had two boxes of greeting cards. After she had transferred 1/5 of the greeting cards in box A to box B, the ratio of the number of greeting cards in box A to the number of greeting cards in box B is 3:5. What was the ratio of the number of greeting cards in box A to the number of greeting cards in box B at first?

Hi

after transfer, Box A : Box B = 3 : 5 = 12u : 20u
Before transfer, Box A = 5/4 x 12u = 15u

Before transfer, Box A : Box B = 15u : 20u-3u = 15: 17

cheers.

[MathIzzzFun]

Angel25:

Pls HELP!!



Roy jogged from his house to the playground and back at 10km/h. He reached home at 12.18pm. If he jogged at 3km/h slower, he would reach home at 1.30pm. If he wanted to reach home at 12.45pm to have his lunch, at what speed did he have to jog?

Thanks!!

Hi

speed ratio, initial : slower = 10 : 7
time ratio, initial : slower = 7: 10

1330-1218 = 72min = 1 1/5h
so 3u = 1.2h, 7u = 1.2/3 x7 = 2.8h = 2h 48min

To reach home at 12.45pm, means to take 1245-1218 = 27min more, ie total time to jog at new speed = 2h 48 min + 27min = 3h 15 min = 3.25h

new speed = 2.8/3.25 x 10 km/h= 112/13 km/h = 8 8/13 km/h

cheers.