P5 Maths - Can anyone help?

Learning is the way SG

Come across this P5 Maths question and need help here to solve the question.

A box contained 50-cent coins and 20-cent coins in the ratio of 2:3. Peter took out four 50-cent coins, exchanged them for 20-cents and put the money back into the box. The ratio then became 2:7. Find the sum of money in the box at first.

skythewood SG

4 50-cent coin equal to 10 20-cent coin

treat X, stuff inside bracket() as boxes

before change

50-cent X X
20-cent X X X

after change

50-cent X X ===> take away 4
20-cent X X X ===> add 10

50-cent (X-2 )(X-2)
20-cent X X X (10)

Learning is the way SG

Your answer is not correct, but the X-2 idea helps me to derive the answer:

4 50-cent coin equal to 10 20-cent coin

treat X, stuff inside bracket() as boxes

before change

50-cent (X+2) (X+2)
20-cent (X+2) (X+2) (X+2)

after change

50-cent X X ===> take away 4
20-cent (X+2) (X+2) (X+2) ===> add 10

50-cent (X-2 )(X-2)
20-cent X X X (10)

Learning is the way SG

Oops..sorry ..accidentally clicl "Reply" before completing the solution.

4 50-cent coin equal to 10 20-cent coin

treat X, stuff inside bracket() as boxes

before change

50-cent (X+2) (X+2)
20-cent (X+2) (X+2) (X+2)

after change

50-cent X X ===> take away 4
20-cent (X+2) (X+2) (X+2) +10 ===> add 10

Rearranging:

50-cent (X)(X)
20-cent (X)(X)(X) (10+2+2+2)

skythewood SG

Your answer is not correct, but the X-2 idea helps me to derive the answer:

4 50-cent coin equal to 10 20-cent coin

treat X, stuff inside bracket() as boxes

before change

50-cent (X+2) (X+2)
20-cent (X+2) (X+2) (X+2)

after change

50-cent X X ===> take away 4
20-cent (X+2) (X+2) (X+2) ===> add 10

50-cent (X-2 )(X-2)
20-cent X X X (10)

refering to underlined steps...

what is that? the 50-cent 2 units have -2... while the 20-cent 3 units have -2.

so is -4 from top, -6 from bottom?

not sure what steps i did wrong... so what is the correct answer?

skythewood SG

Oops..sorry ..accidentally clicl "Reply" before completing the solution.

4 50-cent coin equal to 10 20-cent coin

treat X, stuff inside bracket() as boxes

before change

50-cent (X+2) (X+2)
20-cent (X+2) (X+2) (X+2)

after change

50-cent X X ===> take away 4
20-cent (X+2) (X+2) (X+2) +10 ===> add 10

Rearranging:

50-cent (X)(X)
20-cent (X)(X)(X) (10+2+2+2)

this one make more sense...i believe the question is to find the sum of money at first... so... number of 50-cent according to your units is (x+2)(x+2)... 12.

number of 20-cent is (x+2)(x+2)(x+2).... 18

since x=4.

agree?

Learning is the way SG

The sum of money never change...yes..you got it right.

skythewood SG

The sum of money never change...yes..you got it right.

thanks

skythewood SG

just in case you didn't realise, the $9.60 is wrong.

secretliker SG

If number of 50-cent = 12, number of 20-cent = 18

ratio is 2:3, correct.

After the adding and removing,

50-cent = 8, 20-cent = 22

Ratio is not 2:7

skythewood SG

If number of 50-cent = 12, number of 20-cent = 18

ratio is 2:3, correct.

After the adding and removing,

50-cent = 8, 20-cent = 22

Ratio is not 2:7

try -4 50-cent

plus 10 20-cent

secretliker SG

I see. All along I thought it's removing 4 50-cents and adding 4 20-cents.

Learning is the way SG

Did apply -4 50-cent & +10 20-cent.

After the adding and removing,

50-cent = 8 , 20-cent = 28

($4) , ($5.60)

Sum = $9.60

skythewood SG

Did apply -4 50-cent & +10 20-cent.

After the adding and removing,

50-cent = 8 , 20-cent = 28

($4) , ($5.60)

Sum = $9.60

Come across this P5 Maths question and need help here to solve the question.

baiyun SG

Hi, Hope this helps