Monday, March 12, 2007

more primary 5 maths

Question 1

Toby and Tom had the same amount of pocket money. Each day, Toby spent $12 and Tom spend $15. When Tom had $18 left, Toby had 5 times as much money left as Tom. How much money did each boy have at first?

Question 2

There are a total of 1430 red, blue, green and yellow marbles in a box.

John discovers that if he does all of the following,
* doubles the number of red marbles,
* adds 40 blue marbles,
* removes 30 green marbles and
* removed half the yellow marbles,

he would get the same number of marbles for each colour. How many green marbles are there in the box?


I've actually got the solutions for these questions through a quick call to a maths goddess. I just want to know if these questions are hard or i'm just stupid.

Post your solutions in the comments ok?

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Posted by juni @ 22:54

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Let the starting amount of money each boy has be x.
Let the number of days it takes for Toby to have 5 times the amount that Tom has left be y.

Toby => x - 12y = 5(18)
x - 12y = 90
Tom => x - 15y = 18

Therefore. 90 + 12y = 18 + 15y
72 = 3y
y = 24
Since y = 24, x = 90 + (12x24)
x = 90 + 288
x = 378

Each of them had $378 at first.

Posted by Blogger A|vIn @ 12:55 AM #
 

This comment has been removed by the author.

Posted by Blogger A|vIn @ 1:12 AM #
 

Let the no. of red marbles be r.
Let the no. of blue marbles be b.
Let the no. of green marbles be g.
Let the no. of yellow marbles be y.
Let the no. of each colour of marbles after his action be x.

2r = x
r = x/2

b + 40 = x
b = x - 40

g - 30 = x
g = x + 30

y/2 = x
y = 2x

r + b + g + y = 1430
x/2 + (x - 40) + (x + 30) + 2x = 1430

x/2 + 4x - 10 = 1430
x/2 + 4x = 1440
x + 8x = 2880
9x = 2880
x = 320
g = x + 30
g = 350

There are 350 green marbles in the box.

Posted by Blogger A|vIn @ 1:13 AM #
 

OMG ALVIN!?!?

They're primary 5 kids leh, you can't use this method to solve the questions because they still dunno this method!

Posted by Blogger juni @ 10:36 AM #
 

*raise hands!* teacher I know

Firstly, A model should be drawn.(easier for pri sch kids to visualise!)

SO... Let me try here

R [1 unit ][ (img. 1 unit) ]
B [1 unit ][ ----- | 40 ]
G [1 unit ][--- 1 unit--][30]
Y [1 unit] [---1 unit--- ][1 unit] [---1 unit--- ]

Total: 1430.

So we shall make e equation into 1430 +40 -30

So now:
R [1 unit ]
B [1 unit ][1 unit ]
G [1 unit ][1 unit ]
Y [1 unit ][1 unit ][1 unit ][1 unit ]

so u take 1440 divide by 9... and it gives u 160.
SO 160 * 2 = 320, 320 + 30 = 350 :)

Problem solved!

Posted by Blogger crazyhamster @ 11:11 AM #
 
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