Q&A - PSLE Math
-
MathIzzzFun:
Hilousymum:
pls help
kumar had 50% more bookmarks than leon.
max had 75% as many bookmarks as kumar.
kumar and leon gave max a number of bookmarks in the ratio 3:1.
as a result, max had twice as many bookmarks as before, and leon had 16 bookmarks more than kumar.
how many bookmarks did kumar give to max?
tia
Kumar:Leon --> 3:2
Kumar:Max --> 4:3
Kumar : Leon : Max --> 12 : 8 : 9 --> 48u : 32u : 36u
Max received a total of 36u of bookmarks from Kumar & Leon in ratio of 3:1,
Bookmarks given by Kumar : Leon --> 27u : 9u
Bookmarks left, Kumar : Leon --> 21u : 23u
2u --> 16, 1u --> 8
Bookmarks given by Kumar to Max --> 8 x 27 = 216
cheers.
short simple sweet :goodpost: -
MathIzzzFun:
I'm afraid this is very deep for me. How do I know that I have to multiply 12:8:9 by 4 ? also how do I know that I have to multiply 3:1 by 9 ?
Hilousymum:
pls help
kumar had 50% more bookmarks than leon.
max had 75% as many bookmarks as kumar.
kumar and leon gave max a number of bookmarks in the ratio 3:1.
as a result, max had twice as many bookmarks as before, and leon had 16 bookmarks more than kumar.
how many bookmarks did kumar give to max?
tia
Kumar:Leon --> 3:2
Kumar:Max --> 4:3
Kumar : Leon : Max --> 12 : 8 : 9 --> 48u : 32u : 36u
Max received a total of 36u of bookmarks from Kumar & Leon in ratio of 3:1,
Bookmarks given by Kumar : Leon --> 27u : 9u
Bookmarks left, Kumar : Leon --> 21u : 23u
2u --> 16, 1u --> 8
Bookmarks given by Kumar to Max --> 8 x 27 = 216
cheers. -
mathnoobs:
I'm afraid this is very deep for me. How do I know that I have to multiply 12:8:9 by 4 ? also how do I know that I have to multiply 3:1 by 9 ?[/quote]never mind. I finally figured it out. Still very deep though.
HiMathIzzzFun:
[quote=\"lousymum\"]pls help
kumar had 50% more bookmarks than leon.
max had 75% as many bookmarks as kumar.
kumar and leon gave max a number of bookmarks in the ratio 3:1.
as a result, max had twice as many bookmarks as before, and leon had 16 bookmarks more than kumar.
how many bookmarks did kumar give to max?
tia
Kumar:Leon --> 3:2
Kumar:Max --> 4:3
Kumar : Leon : Max --> 12 : 8 : 9 --> 48u : 32u : 36u
Max received a total of 36u of bookmarks from Kumar & Leon in ratio of 3:1,
Bookmarks given by Kumar : Leon --> 27u : 9u
Bookmarks left, Kumar : Leon --> 21u : 23u
2u --> 16, 1u --> 8
Bookmarks given by Kumar to Max --> 8 x 27 = 216
cheers. -
mathnoobs:
I'm afraid this is very deep for me. How do I know that I have to multiply 12:8:9 by 4 ? also how do I know that I have to multiply 3:1 by 9 ?[/quote]
HiMathIzzzFun:
[quote=\"lousymum\"]pls help
kumar had 50% more bookmarks than leon.
max had 75% as many bookmarks as kumar.
kumar and leon gave max a number of bookmarks in the ratio 3:1.
as a result, max had twice as many bookmarks as before, and leon had 16 bookmarks more than kumar.
how many bookmarks did kumar give to max?
tia
Kumar:Leon --> 3:2
Kumar:Max --> 4:3
Kumar : Leon : Max --> 12 : 8 : 9 --> 48u : 32u : 36u
Max received a total of 36u of bookmarks from Kumar & Leon in ratio of 3:1,
Bookmarks given by Kumar : Leon --> 27u : 9u
Bookmarks left, Kumar : Leon --> 21u : 23u
2u --> 16, 1u --> 8
Bookmarks given by Kumar to Max --> 8 x 27 = 216
cheers.
Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions. -
Zack7:
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.
Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions. -
mathnoobs:
Hi
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.Zack7:
Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions.
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. -
mathnoobs:
well , i think that algebra is the way to go especially since they now learn it in p6.
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.Zack7:
Ratios are about scaling. You don't have to multiply them, just that u will b working with fractions.
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 -
Hi Zack7 & MathIzzzFun,
:thankyou: -
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 -
Winx5015:
HiAnyone 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
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.
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