ANOTHER PRI SCH MATHS QN

[Joseph22]

The assumption of the unit remaining the same value after giving away 78 or adding 78 is not logical. Or am I missing something?

you missing a lot of thing.

 

you draw up the whole thing first.

 

then you can see clearly.

[1fast1]

David has 5 times as many marbles as Tim. If he gives 78 marbles to Tim, he will still have twice as many marbles as Tim.

 

1) how many marbles do they have altogether?

2) how many more marbles does DAvid have than Tim now?

 

The first part is unambiguous. The answer is 468, as others have stated.

 

The second part is more tricky. I interpret the "now" as being the present (initial) condition - before David has given any marbles to Tim. Recognise that the "if" signifies a hypothetical - it doesn't mean he's actually done it.

 

So the answer to the second part is 312.

 

Method:

 

Let Tim's initial marble set be represented by one unit (square, circle, whatever). Then David has 5 units. It's obvious that if he donates one unit to Tim, he'll have 4 and Tim will have 2 - so David will have twice Tim's complement of marbles. Hence one unit = 78. Answer to 1) is total no. of units*78 = 6*78 = 468. Answer to 2) is (5-1) units*78 = 4*78 = 312.

 

To cover myself (in case the damn question setter meant the other scenario - after David has given 78 to Tim), I would also include the answer to that i.e. (4-2)*78 = 2*78 = 156. This way, teacher just cannot mark me wrong. Yes, I was damn kiasu even as a kid.

 

Parsing the poor wording of these questions is enough to make anyone lose their marbles!

Edited October 18, 2011 by Turboflat4

[Tonyng]

 

Anyone tried out the question on Siri yet?