Tutor MathsGuru: Ask me for your burning Maths questions!

[Dharma]

Herbie:

I have one qn.


There were some boys and girls in a room.
If 24 boys leave the room, the total no. of students who remained in the room will be 7 times theno. of boys who remained the the room.
If 12 girls leave the room, the total no. of students who remained in the room will be 4 times the no. of boys.

How many students are there in the classroon?

Tq

Boys at first = 1u + 24 = 1p ………… (1)
Girls at first = 6u = 3p + 12 ………… (2)

6u = 3(1u + 24) + 12
3u = 84
1u = 28

No. of students in classroom = 7u + 24 = 7(28 ) + 24 = 220

[Herbie]

Hi Dharma,


I dun understand how you form the eqn 1 and 2.

Can explain?

Tx

[livewith_vanilla]

Source: School Paper (P6)


Questions:

1) 65% of the animals on a farm were cows and the rest were goats. When 240 more cows and goats were added to the farm, the percentage of cows increased by 20% and the number of goats doubled. How many goats were there on the farm at first?

2)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 number 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?

TIA!

[Dharma]

Herbie:

Hi Dharma,


I dun understand how you form the eqn 1 and 2.

Can explain?

Tx

If 24 boys leave the room:

At last
Boys : 1u
Girls : 6u

At first
Boys : 1u + 24
Girls : 6u

If 12 girls leave the room

At last
Boys : 1p
Girls : 3p

At first
Boys : 1p
Girls : 3p + 12

The number of boys and girls at first must be the same

1u + 24 = 1p -------------- (1)
6u =3p + 12 --------------- (2)

Solve to find the no. of boys and girls

[Dharma]

[Editor's note: Topic selected & edited for http://www.kiasuparents.com/kiasu/content/some-math-questions-and-answers.]

livewith_vanilla:

Source: School Paper (P6)


Questions:

1) 65% of the animals on a farm were cows and the rest were goats. When 240 more cows and goats were added to the farm, the percentage of cows increased by 20% and the number of goats doubled. How many goats were there on the farm at first?

2)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 number 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?

TIA!

1)
At first
Cows => 65% = 65u
Goats => 35% = 35u

At last
Cows => 65u + 13u = 78u
Goats => 35u + 35u = 70u

13u + 35u = 48u = 240
1u = 5
No. of goats at first = 35u = 35 x 5 = 175


2)
If 20 black marbles removed
At lastBlack : 1u
White : 6u

At first
Black : 1u + 20
White : 6u

If 50 white marbles removed
At last
Black : 1p
White : 4p

At first
Black : 1p
White : 4p + 50

1u + 20 = 1p --------------- (1)
6u = 4p + 50 ----------------(2)
6u = 4( 1u + 20 ) + 50
6u = 4u + 130
2u = 130
1u = 65

No. of marbles in the bag = 7u + 20 = 7(65 ) + 20 = 475

[livewith_vanilla]

Dharma:

livewith_vanilla:

Source: School Paper (P6)


Questions:

1) 65% of the animals on a farm were cows and the rest were goats. When 240 more cows and goats were added to the farm, the percentage of cows increased by 20% and the number of goats doubled. How many goats were there on the farm at first?

2)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 number 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?

TIA!

1)
At first
Cows => 65% = 65u
Goats => 35% = 35u

At last
Cows => 65u + 13u = 78u
Goats => 35u + 35u = 70u

13u + 35u = 48u = 240
1u = 5
No. of goats at first = 35u = 35 x 5 = 175


2)
If 20 black marbles removed
At lastBlack : 1u
White : 6u

At first
Black : 1u + 20
White : 6u

If 50 white marbles removed
At last
Black : 1p
White : 4p

At first
Black : 1p
White : 4p + 50

1u + 20 = 1p --------------- (1)
6u = 4p + 50 ----------------(2)
6u = 4( 1u + 20 ) + 50
6u = 4u + 130
2u = 130
1u = 65

No. of marbles in the bag = 7u + 20 = 7(65 ) + 20 = 475

Thanks!

[anonymus]

Dharma:

Almighty:

[quote=\"mathsguru\"]
Hi Almighty,

I don’t really understand what you are trying to say but we know that that the radius of the circle is 14cm and the radius of 14cm is also the side of the small equilateral triangles.

Perimeter of the shaded part
= Length of the 3 sides of a triangle + Curved length of the semicircle
= ( 14 x 3 ) + ( 22/7 x ½ x 14 x 2 )
= 42 + 44
= 86

The perimeter of the shaded part = 86cm

[/quote]Let me put it in a simpler manner.
Pls see the highlighted 14 X 2 in your solution.The straight line of the shaded semicircle is 14 cm. Its the diameter of that semicircle also. Then y do u mulitply by 2? Please see highlighted portion of my solution on top.hope i am clear. Please dharma..dont get irritated..pls explain...

[991narnia]

Pls help me with this question



1. Four children, Eugene, Fann, Grace and Herman, each have some stickers. The number of stickers that Eugene has is 1/2 of the total number of stickers that Fann, Grace, and Herman have. The number of stickers that Fann has is 1/4 of the total number of stickers that Eugene, Grace and Herman have. The number of stickers that Grace has is 2/3 of the total number of stickers that Eugene, Fann, and Herman have. If Herman has 47 stickers, how many stickers should Grace give to Fann so that Eugene and Fann have the same number of stickers?

[Dharma]

anonymus:

Dharma:

[quote=\"Almighty\"]
Let me put it in a simpler manner.
Pls see the highlighted 14 X 2 in your solution.The straight line of the shaded semicircle is 14 cm. Its the diameter of that semicircle also. Then y do u mulitply by 2? Please see highlighted portion of my solution on top.hope i am clear. Please dharma..dont get irritated..pls explain...

[/quote]Hi Almighty and anonymus,

The highlighted in blue “ … 14 x 2” is actually the diameter of a circle.

Diameter of circle = pi x Diameter

The straight lines in the semicircle form equilateral triangles within the circle. Here, if you notice carefully, the sides of the triangles is the length of the radius of the circle and NOT the diameter. I multiplied the radius (14cm) by 2 to get the diameter of the circle.

Now if you notice the highlighted length of the figure above is actually

Total length of 3 equal straight lines + The curved length of the semicircle
= (14cm x 3) + (pi x Diameter x 1/2)
= 42cm + ( 22/7 x 28cm x ½)
= 42cm + 44cm
= 86cm

OR

Based on Almighty’s workings:

If you take the perimeter (highlighted) of 1 sector; you need to find the arc length of the curve with an angle of 60 degrees plus the length of side of the triangle (14cm)

Arc length = 60/360 x pi x Diameter = 1/6 x 22/7 x 2 x 14cm = 44/3cm
Perimeter of the highlighted part of 1 sector = (44/3 + 14)cm
Perimeter of the highlighted part of 3 sectors = (44/3 + 14)cm x 3 = 44cm + 42cm = 86cm

[liketoeat]

Dharma:

liketoeat:

Here's another question.


Each day, Mike saves $0.50 while Carol saves $0.30 more than her. Carol starts saving 6 days after Mike. She has $17.40 more than Mike now. How much does Mike save now? (Ans: $37)

Carol starts saving from Day 6 onwards.
Mike saved $ 3.00 ($0.50/day x 6 days) from Day 1 to Day 5

Day 6 to now; Carol saved $ 20.40 ($17.40 + $3.00) more than Mike.

No. of days from Day 6 to now = $20.40/ ($0.30/day) = 68 days

Amount Mike saved from Day 1 until now = $ 3.00 + ($0.50/day x 68 days) = $37.00

Hi Dharma,

I don't understand why Day 1 to Day 5 is 6 days. Please help me to understand. Thank you.