Q&A - PSLE Math

[Zack7]

mathnoobs:

Zack7:

Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions.

yes, but it is not easy to see the scaling factor, until you go through the entire question, mull through it and figure out which numbers you need to equalize. In this case, have to scale twice, so not so easy to see upfront. I think under exam conditions, very difficult to see how to scale it so that the relevant numbers are equal. Even under non exam conditions, for me, it was difficult to see which numbers can be equalized and thus scaling is applied.

well , i think that algebra is the way to go especially since they now learn it in p6.

algebra is the main tool after primary school and it can also solve almost all of the primary school questions.

so it would be good for your child to associate and familiarize with it now

[lousymum]

Hi Zack7 & MathIzzzFun,


:thankyou:

[Winx5015]

Anyone can help me with these questions?


(1). The distance between Town A and Town B is 40km. Mr Goh drove from Town B towards Town A at the speed of 85km/h. At the same time, Mr Wong drove from Town A towards Town B at 75km/h. How many hours later would they meet?

(2). Adrian and Bob started driving at the same time. Bob took 6 hours to complete his journey while Adrian took 9 hours to complete his. After 3 hours, the two men were left with the same distance to complete. What is the ratio of the distance of Bob's journey to the distance of Adrian's journey?

(3). A man travels from Town X to Town Y at 4km/h and from Town Y to Town X at 6km/h using the same route. The whole journey takes 45 minutes. Find the distance from Town X to Town Y.

Thank you

[MathIzzzFun]

Winx5015:

Anyone can help me with these questions?


(1). The distance between Town A and Town B is 40km. Mr Goh drove from Town B towards Town A at the speed of 85km/h. At the same time, Mr Wong drove from Town A towards Town B at 75km/h. How many hours later would they meet?



Thank you

Hi
Q1.
Time taken to meet = distance / \"closing speed\" = 40/(85+75) h =1/4h = 15 min

**Closing speed --> In hour, total distance covered = 75 + 85 = 160km ie the gap between Mr Wong and Mr Goh is reducing at the speed of 160km/h. So, time taken for gap to reduce to zero ie at meeting point is equal to the time taken to travel 40 km at 160km/h**

cheers.

[MathIzzzFun]

Winx5015:

Anyone can help me with these questions?


(2). Adrian and Bob started driving at the same time. Bob took 6 hours to complete his journey while Adrian took 9 hours to complete his. After 3 hours, the two men were left with the same distance to complete. What is the ratio of the distance of Bob's journey to the distance of Adrian's journey?

Thank you

Hi
In 3 hours,
Distance covered by Bob --> 3/6 = 1/2 Bob's journey
Distance covered by Adrian --> 3/9 = 1/3 Adrian's journey.
Since both had same distance left to complete,
1/2 Bob's journey = 2/3 Adrian's journey
Bob's journey : Adrian's journey = 4 : 3

cheers.

[MathIzzzFun]

Winx5015:

Anyone can help me with these questions?



(3). A man travels from Town X to Town Y at 4km/h and from Town Y to Town X at 6km/h using the same route. The whole journey takes 45 minutes. Find the distance from Town X to Town Y.

Thank you

Hi

speed ratio, x->y : y->x = 4 : 6 = 2:3
time ratio, x->y : y->x = 3u : 2u, total time --> 5u
5u --> 45 min, 3u --> 27 min
Distance between X-Y
= 4 km/h x 27 /60 h (x->y)
= 6 km/h x 18/60 h (y->x)
= 1.8 km

cheers.

[mathnoobs]

MathIzzzFun:

mathnoobs:

[quote=\"Zack7\"]
Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions.

yes, but it is not easy to see the scaling factor, until you go through the entire question, mull through it and figure out which numbers you need to equalize. In this case, have to scale twice, so not so easy to see upfront. I think under exam conditions, very difficult to see how to scale it so that the relevant numbers are equal. Even under non exam conditions, for me, it was difficult to see which numbers can be equalized and thus scaling is applied.

Hi

students learn in lower primary how to \"scale\" using models. eg. Alice had twice as much money as Mary. If they had $30 altogether, how much did each have?

The model drawing will show 2 blocks for Alice, 1 block for Mary. Total 3 blocks representing $30

eg. The number of red marbles to the number of blue marbles in a box is in the ratio of 2 : 7. If there are 63 marbles altogether, how many red marbles are there ?
The model drawing will show 7 blocks for blue marbles, 2 blocks for red marbles, total 9 blocks representing 63.

In the question above, when we arrive at the ratio Kumar: Leon: Max-->12:8:9, we can work with these numbers directly ie 12u:8u:9u

Max has 9u. Since he had twice after receiving the bookmarks from the others, he received 9u.
So, total number contributed by both kumar and leon is 9u, in the ratio of 3:1 --> back to the examples above: Kumar 3 blocks, Leon 1 block, total 4 blocks for 9u, so 1 block --> 9u/4

Kumar gave 3 blocks --> 3x 9u/4 = 27u/4
Leon gave 1block --> 9u/4

Left, Kumar : Leon --> 12u-27u/4 : 8u-9u/4 --> 21u/4 : 23u/4 --> 21u:23u ... so we get to the same final ratio. the only difference is that when we work with the numbers directly, we will have to work with fractions - which many students dislike

good night !

cheers.[/quote]Hi MathIzzzfun
thank you for your example. It has helped me in understanding scaling. I guess I'll need more practise in this area to be really familiar with the concept. For simple one step scaling, I'm alright, but for the scaling as required by this problem sum, it is a little bit more difficult to grasp.

[Winx5015]

MathIzzzFun



:thankyou:

[Ngserene617]

Winx5015:

MathIzzzFun



:thankyou:

Hi, pls help on these questions:

1. Malcom's salary in January was $2800. He saved 3/8 of it. In February, his salary increased by 25% and he saved 35% of it. What was the percentage increase in Malcom's savings from January to February? ( Give your answer to the nearest 1%)

2. Ms Sumei spent $672 of her savings on clothing and 3/8 of the remainder on cosmetics. She had 1/4 of her savings left. What was Ms Sumei's original amount of savings?

Thanks

[MathIzzzFun]

Winx5015:

MathIzzzFun



:thankyou:

u r welcome

cheers.