Q&A - PSLE Math

[speedmaths.012624com]

2DMommy:

Please help me with these :


Find the sum of 35 + 37 + 39 + 41 + 43 ........ + 231 + 233.

What is the short cut to this question ?

Thank you.

Hi,

One possible shortcut:
(copied from the 2 books: Go For A* Vol 1a and Vol 2)

Average = Sum / (Number of Terms)

Sum = (Number of Terms) x Average

Number of Terms = 100
(there are 100 numbers from 35, 37, ... to 233)

Average = (35 + 233) / 2 = 134

Sum = 100 x 134 = 13400.

Hope this helps.

Cheers

speedmaths.com

.

[tianzhu]

Tiramisu Coco:

Hi, pls help with this qtn. Thks!


http://m.flickr.com/photos/82618212@N07/7837766706/lightbox/

Hi

A similar question has been discussed in one of the earlier posts, but I can't locate it now.

There are a few ways to solve it.

One possible way.

Radius of circle -------( a+b-c)/2 -------(18+24-30)/2 ------ 6 cm

Best wishes

[AJH]

Hi. I nd help with this ques.


Brendan and Raidah saved $6475.60 altogether. 2/5 of Brendan’s savings was $341.50 more than 1/5 of Raidah’s savings. How much more money than Brendan did Raidah save?

Can’t seem to get the ans - $1020.20. Thank you.

[MathIzzzFun]

AJH:

Hi. I nd help with this ques.


Brendan and Raidah saved $6475.60 altogether. 2/5 of Brendan's savings was $341.50 more than 1/5 of Raidah's savings. How much more money than Brendan did Raidah save?

Can't seem to get the ans - $1020.20. Thank you.

1/5 of Raidah's savings --> 2 units,
Raidah's savings --> 10 units
2/5 of Brendan's savings --> 2 units + $341.50 = 2 x (1 unit + $170.75)
Brendah's savings --> 5 units + $853.75

Total --> 15 units + $853.75 = $6475.60
5 units --> $1873.95

Raidah's savings MINUS Brendan's savings
= 5 units - $853.75
= $1873.95 - $853.75 = $1020.20

cheers.

[Bunny27]

Hi, can someone pls help on this question


1. Habri had some 20cents coins and 50cents coins.
He spent 1/4 of his 20cents coins and 40% of his 50cents coins.
The value of 20cents coins left was the same as the value of 50cents coins left. If the difference between the value of 20cents coins and the value of 50cents coins he had at first was $12, how much did Habri have at first?

TIA

[ET-PH]

charsen:

superksmum:

Hi please help on this question (Henry Park Prelim 2011, question 16).


Mr Lee took 7 hours to travel from Town A to Town B while Mr Wong took 8 hours to travel from Town B to Town A. Both of them did not change their spped throughout the journey. Both of them started off at the same time and moved towards each other. 3 hours later, they were 110km apart. What was the speed Mr Lee was driving?

Thank you.

Hi
In 3 hours, lee drove 3/8 of the journey.At the same time,wong took 3/7 of the journey.So,we should make the denominators 8 and 7 to be 56 since the distance in both is common.

Lee travelled 24U and wong travelled 21U.
56u-24U-21U=11U
11U-110km
1U-110/11=10km
Distance lee travelled--->10x24=240km
Lee's speed------>240/3=80km/h(ANS)

Hi Charsen,

I stuck with this question too, can you explain how you get 3/8 of the journey for Lee and 3/7 of the journey for Wong. Thanks.

[ET-PH]

Hi, I need help on HPPS 2011 Prelim Qn 17.


There were 1000 students at the parade ground and indoor sports hall. 40% of the 600 students at the parade ground were girls. 60% of the students at the indoor sports hall were girls. After some students in both the venues moved from one venue to the other, 30% of the students in the parade ground and 70% of the students at the indoor sports hall were girls. How many students were there in the indoor sports hall after the movement had taken place ? Thanks.

[MathIzzzFun]

ET-PH:

Hi, I need help on HPPS 2011 Prelim Qn 17.


There were 1000 students at the parade ground and indoor sports hall. 40% of the 600 students at the parade ground were girls. 60% of the students at the indoor sports hall were girls. After some students in both the venues moved from one venue to the other, 30% of the students in the parade ground and 70% of the students at the indoor sports hall were girls. How many students were there in the indoor sports hall after the movement had taken place ? Thanks.

this was discussed - http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=7690

cheers.

[MathIzzzFun]

ET-PH:

charsen:

Hi please help on this question (Henry Park Prelim 2011, question 16).


Mr Lee took 7 hours to travel from Town A to Town B while Mr Wong took 8 hours to travel from Town B to Town A. Both of them did not change their spped throughout the journey. Both of them started off at the same time and moved towards each other. 3 hours later, they were 110km apart. What was the speed Mr Lee was driving?

Thank you.
Hi
In 3 hours, lee drove 3/8 of the journey.At the same time,wong took 3/7 of the journey.So,we should make the denominators 8 and 7 to be 56 since the distance in both is common.

Lee travelled 24U and wong travelled 21U.
56u-24U-21U=11U
11U-110km
1U-110/11=10km
Distance lee travelled--->10x24=240km
Lee's speed------>240/3=80km/h(ANS)

Hi Charsen,

I stuck with this question too, can you explain how you get 3/8 of the journey for Lee and 3/7 of the journey for Wong. Thanks.

there is a typo error... Mr Lee travelled 3/7 of journey, Mr Wong travelled 3/8 of journey

Distance between AB --> 56 units
Mr Lee took 7 hours to travel from A to B,
so in 3 hours, distance travelled --> 3/7 x 56 units = 24 units

Mr Wong took 8 hours to travel from B to A
so, in 3 hours, distance travelled --> 3/8 x 56 units = 21 units

Total distance between A & B
= 21 units + 24 units + 110 km --> 56 units
11 units --> 110 km
1 unit --> 10 km
Mr Lee's speed --> distance AB/ time to travel AB = 56 x 10 / 7 = 80 km/h

cheers.

[MathIzzzFun]

Bunny27:

Hi, can someone pls help on this question


1. Habri had some 20cents coins and 50cents coins.
He spent 1/4 of his 20cents coins and 40% of his 50cents coins.
The value of 20cents coins left was the same as the value of 50cents coins left. If the difference between the value of 20cents coins and the value of 50cents coins he had at first was $12, how much did Habri have at first?

TIA

3/4 of value of 20-cent coins = 3/5 of value of 50-cent coins
At first,
value of 20-cent coins : value of 50-cent coins --> 4u : 5u -- total value --> 9u
1u --> $12
Total amount of money Habri had at first --> 9 x $ 12 = $108

cheers.