P5 math problem

dibilo SG

The number of Joe's marbles to Mary's marbles was 2:3. After Jon bought 8 marbles and Mary lost 5 marbles, Jon now has 4/5 as many marbles as Mary. How many marbles do they have at first?

using algebra, I can solve it

10u + 8 = 4/5(15u - 5)

10u + 8 = 12u - 4

2u = 12

u = 6

6 x 25 = 150

How do you do it "simpler"?

Only-Way-4-Destiny! SG

Let the number of marbles Joe has be x

Mary's number of marbles = 3/2 x = 1½ x

(x+8)/(1½ x-5) = 4/5

Cross Multiply

4(1½x -5) = 5(x+8)

6x - 20 = 5x + 40

6x - 5x =40 + 20

x = 60

x+1½ x = 2½ x

2½ x = 2½(60)

2½ x = 150

They have 150 marbles at first.

Lee012lee SG

PSLE maths question uses algebra with cross-multiply, equation to solve the

question.

The PSLE student will not be able to understand the answers lah. D.

They are taught to use model drawing method only to solve the question lor.

Only-Way-4-Destiny! SG

yea. Sadly no cos, sin, tan or quadratic or cubic equations.

Don© SG

I find it gay that primary school math is getting tougher and tougher.

What sort of childhood will the next generation grow up with.

baiyun SG

Hope this helps.

Lee012lee SG

Yes, baiyun has provided an excellent answer with a very beautiful presentation of

the answer in model drawing method to which a PSLE maths student will

understand.

Only-Way-4-Destiny! SG

Mine oso easy to understand.

SBS n SMRT SG

can aslo use guess and check

Lee012lee SG

Mine oso easy to understand.

PSLE maths students have not learnt secondary school algebra.

They are only taught the drawing model and the guess and check methods to solve

the question.

SunArtist SG

It takes me a while to understand Baiyun's solution. Anyone knows if this question is considered tough or average for P5?