Tutor MathsGuru: Ask me for your burning Maths questions!

[corneyAmber]

Almighty:

Hi,

Another doubt..Pl.help!!!

Molly's monthly salary was $3600.She spent 1/10 of it on food.1/3 more of it on clothes than on food and 3/4 of the remainder on rent.She saved the rest of the money.
a) What %age of her money did she spend on rent? Ans gn is 35% but i ger 57.5%

For amt spend on clothes : I did in this way:
4/3/X $360 = $480
Ans key has done like this:
360+(1/3X3600) = $1560

Y is that i should not do in my way if the ans key is correct. Please let me know the correct answer.
According to me the answer i get for a) 57.5%

Hi Almighty,

The reason why you calculate the clothes $ wrongly because the \"of it\" in both instances refer to the total salary $3600. So you must take 1/3*3600 instead of 1/3*360(which is the $$ for food only)

[Almighty]

Dharma:

Almighty:

[quote=\"Dharma\"]
June
Salary => 100% (10u)
Spend => 40% (4u)

July
Salary => 80% x 10u = 8u
Spend => 4u
% of salary spent in July = 4u/8u x 100% = 50%

\"


I followed this way. Pl.Dharma, can u explain (step by step) y i should not do this way.

June Spent is 40% of 100
July spent is 40% X80(80 = 20% less than june salary= Total salary in july) = 32%
So, % of july salary she spend = 32/80 X100% = 40%
Sorry to have troubled you n thanks in advance..

Hi Almighty,

Han spent the SAME AMOUNT of money in June as in July.

Therefore the spending in July is 4u (40% of 10u) and NOT 40% of 8u.[/quote]Oh!!! Thanks Dharma.I got it now I should read as \"Han spent the same 40% of her salary in June\" and not as \"same 40% of her salary \"Now i feel very silly... Thankyou for all who tried 2 explain me...

[Almighty]

ksi:

Almighty:

Hi,

Another doubt..Pl.help!!!

Molly's monthly salary was $3600.She spent 1/10 of it on food.1/3 more of it on clothes than on food and 3/4 of the remainder on rent.She saved the rest of the money.
a) What %age of her money did she spend on rent? Ans gn is 35% but i ger 57.5%

For amt spend on clothes : I did in this way:
4/3/X $360 = $480
Ans key has done like this:
360+(1/3X3600) = $1560

Y is that i should not do in my way if the ans key is correct. Please let me know the correct answer.
According to me the answer i get for a) 57.5%

Hi Almighty,

The reason why you calculate the clothes $ wrongly because the \"of it\" in both instances refer to the total salary $3600. So you must take 1/3*3600 instead of 1/3*360(which is the $$ for food only)

Thanks Ksi 4 yr explanation. But, I am still not clear..How can v read it as 1/3 more than the mnthly salary on clothes?Can u explain in detail?

[Almighty]

Hi Almighty,


The reason why you calculate the clothes $ wrongly because the \"of it\" in both instances refer to the total salary $3600. So you must take 1/3*3600 instead of 1/3*360(which is the $$ for food only)[/quote]

Thanks Ksi 4 yr explanation. But, I am still not clear..How can v read it as 1/3 more than the mnthly salary on clothes?Can u explain in detail?[/quote]

Hi Dharma/KSI,

HOw can he spent more than what he gets as salary?We cannot assume he might hv savings in tht mnth r so .Right?Is my question clear? Y noone replied to me?How can v read it as [color=red]1/3 more than the mnthly salary?Hope i am clear.

[Almighty]

Almighty:

Hi Almighty,


The reason why you calculate the clothes $ wrongly because the \"of it\" in both instances refer to the total salary $3600. So you must take 1/3*3600 instead of 1/3*360(which is the $$ for food only)

Thanks Ksi 4 yr explanation. But, I am still not clear..How can v read it as 1/3 more than the mnthly salary on clothes?Can u explain in detail?[/quote][/color]

Hi Dharma/KSI,

HOw can he spent more than what he gets as salary?How can v read it as 1/3 more than the mnthly salary?
Hi Maths Guru,
Can i atleast get your help on this?How can v read it as 1/3 more than the mnthly salary.I dont want this mistake of mine in reading 2 b repeated.Any help to explain?

[YLH88]

Hi all,


Need help with the following speed questions. :? So sorry for the long list as I'm trying to polish my DS on his speed questions

1) Ali and Boris walked from their homes to school.
Ali started walking from point X at a speed of 120 m/min.
At 9.05am, Ali reached point Y and at the same time Boris started walking from Point Y towards the school.
At 9.15am, Boris was 100m ahead of Ali.
a) Find Boris's speed
b) If Boris reached the school 2 min ahead of Ali, find the distance Boris covered from point Y to the school. Express your answer in kilometres.

(I'm able to get the answer for part a which is 130 m/min, but can't do part b)


2) A car and a lorry were heading from Town A to Town B.
When the car overtook the lorry, they were 375 km away from Town B.
The car arrived 1 h 15min earlier than the lorry which was still 75 km away from Town B.
a) Find the average speed of the lorry.
b) Find the average speed of the car.


3) Car A and Car B left Town Y at the same time, heading in the opposite direction.
Car A headed for Town Z while Car B left for Town X.
The speed of Car B was 20 km/h faster than Car A.
After 1/2 h, Car A had completed 2/3 of its journey while Car B had completed 1/2 of its journey.
The two cars were also 110 km apart.
a) Calculate the speed of Car A.
b) How far was Car B from Town X when Car A reached its destination ?


4) At 11am, Mrs Chong left Town X for Town Y, driving at a constant speed.
2 hours later, Mrs Tan also left Town X for Town Y.
At 5pm, Mrs Tan overtook Mrs Chong.
The average speed of Mrs Tan was 32 km/h faster than the average speed of Mrs Chong.
a) Find the average speed of Mrs Chong.
b) Mrs Tan was 26 km away from Town Y at 5pm. Find the distance between Town X and Town Y.


5) A car, travelling at a constant speed, took 9 hours to travel from Town Y to Town Z.
A lorry, travelling at a constant speed, took 18 hours to travel from Town Z to Town Y.
Both vehicles started at the same time and they met when they were 180 km from Town Z.
a) Find the distance between the two towns.
b) Find the speed of the car.


6) Mark can climb uphill at an average speed of 2km/h and go downhill at an average speed of 6km/h. Going first uphill and then downhill, without stopping and using the same route, what will his average speed be for the entire trip ?


7) Wei Qiang walked up a flight of steps at an average speed of 50 m/min.
When he reached the top, he ran down the same flight of steps at a speed of 200 m/min. If he took a total of 1 min to walk up and run down, how many seconds did he take to walk up the flight of steps ?


Thank you very very much !

[YLH88]

[quote]
1) For time questions, is it true that the answer must be left in fraction and not decimal ? My DS wrote the answer as 37.5 h and the teacher marked him wrong. She said the answer should be 37 1/2 h. Thus, would like to check what is the practice for PSLE ? which is correct in PSLE context, 37.5 h or 37 1/2 h ?[/quote]Hi,

Regarding the question on whether to leave the time in fraction or decimal, I'm not able to get through MOE hotline, but I have consulted few teachers. Their answer are the same : Should leave the time answer in fraction even if it is 1/2 hr. Most of the time, the teacher will advise the students not to leave in decimal unless the question said so.

Regards

[Vanilla Cake]

YLH88:

1) Ali and Boris walked from their homes to school.

Ali started walking from point X at a speed of 120 m/min.At 9.05am, Ali reached point Y and at the same time Boris started walking from Point Y towards the school.At 9.15am, Boris was 100m ahead of Ali.
a) Find Boris's speed
b) If Boris reached the school 2 min ahead of Ali, find the distance Boris covered from point Y to the school. Express your answer in kilometres.

From 9.05 am to 9.15 am, time = 10 min
Distance travelled by Ali @ 120 m/min from Pt Y= 120 m/minx10min = 1200 m
Distance travelled by Boris from Pt Y = (1200+100)m = 1300m
(a) Boris average speed = 1300÷10 = 130 m/min

Distance between Pt Y to school = D
D/130+2 = D/120
(D+260)/130 =D/120
130D=120D+31200
10D=31200
D=3120m = 3.12 km
(b)Distance between Boris covered from point Y to the school = 3.12 km

OR

Ratio of speed
Ali : Borris
120 : 130
12 : 13

Ratio of time
Ali : Borris
13 : 12

Difference = (13-12)u = 1u = 2min ( Boris reached the school 2 min ahead of Ali)
For Ali's case @ 120 m/min, distance travelled = 13ux120=13x2x120=3120m = 3.12 km
For Borris's case @ 130m/min, distance travelled = 12ux130 =12x2x130=3120m = 3.12 km

YLH88:

2) A car and a lorry were heading from Town A to Town B. When the car overtook the lorry, they were 375 km away from Town B.
The car arrived 1 h 15min earlier than the lorry which was still 75 km away from Town B.
a) Find the average speed of the lorry.
b) Find the average speed of the car.

1 h 15 min = 1¼h
75÷1¼h=60 km/h
(a) Average speed of lorry = 60 km/h

375÷60=6¼h
6¼h-1¼h=5h
(b) Average speed of car = 375÷5 = 75 km/h

[Vanilla Cake]

YLH88:

4) At 11am, Mrs Chong left Town X for Town Y, driving at a constant speed.2 hours later, Mrs Tan also left Town X for Town Y.At 5pm, Mrs Tan overtook Mrs Chong.The average speed of Mrs Tan was 32 km/h faster than the average speed of Mrs Chong.

a) Find the average speed of Mrs Chong.
b) Mrs Tan was 26 km away from Town Y at 5pm. Find the distance between Town X and Town Y.

Headstart by Mrs Chong was 2 hours ahead of Mrs Tan and Mrs Tan took 4 hours to catch up with Mrs Chong. (average speed of Mrs Tan was 32 km/h faster than the average speed of Mrs Chong)

Distance travelled by Mrs Chong in 2 hours = 32x4=128 km
(a) Average speed of Mrs Chong was 128÷2 = 64 km/h

Time taken for Mrs Chong from 11 am to 5 pm = 6 hours
Distance travelled by Mrs Chong in 6 hours = 6x64 = 384 km
(b) Distance between Town X and Town Y = 384km+26km = 410 km

[Herbie]

I have a question which need help. ACS 2009 Paper 2 Q18


There are some black and white marbles in a bag.
If 20 black marbles are removed from the bag, the total number of marbles left will be 7 times the no. of black marbles left.
If 50 white marbles are removed from the bag, the total number of marbles left will be 5 times the number of black marbles left.

How many marbles are there in the bag?

Tx