Q&A - PSLE Math

[kwcllf]

Sorry, don’t have the diagram to show.


For a Triangular pyramid:
The first level needs 3 sticks to form (1 single triangle)
The second level needs 9 sticks to form (2 triangles as base)
The Third level needs 18 sticks to form (3 triangles as base)
The fourth level needs 30 sticks to form (4 triangles as base) …etc

How many sticks are needed to form a 10-level pyramid?

Thanks

[Zhu99]

kwcllf:

Sorry, don't have the diagram to show.


For a Triangular pyramid:
The first level needs 3 sticks to form (1 single triangle)
The second level needs 9 sticks to form (2 triangles as base)
The Third level needs 18 sticks to form (3 triangles as base)
The fourth level needs 30 sticks to form (4 triangles as base) .........etc

How many sticks are needed to form a 10-level pyramid?

Thanks

1 --- 3 x 1
2 --- 3 x 1 + 3 x 2 = 3 x (1+ 2) =9
3 --- 3 x 1 + 3 x 2 + 3 x 3 = 3 x (1 + 2 + 3) = 18

10 --- 3 x (1 + 2 + 3+ 4 + 5 + 6 + 7 + 8 + 9 + 10) = 3 x 55 = 165

165 stickers are needed to form a 10-level pyramid.

[24hr_mum]

can someone explain to me nanyang paper 2 q17.

[kwcllf]

Hi Zhu99,


Thanks very much!

[nounou]

Please help. St Hilda Prelim 2012 Q5. 2 mark Q only. Why so difficult? Luan liao! :siao: :stupid: :xedfingers:

:thankyou: :thankyou: :thankyou: http://i50.tinypic.com/v3n22o.jpg\">

[tianzhu]

Treelodge:

Please help. St Hilda Prelim 2012 Q5. 2 mark Q only. Why so difficult? Luan liao! :siao: :stupid: :xedfingers:

:thankyou: :thankyou: :thankyou: http://i50.tinypic.com/v3n22o.jpg\">

Hi

As seen from the table, numbers which are multiples of 10 are in column C.

Now study each row, take row 5.

The number 65 in B is 5 less than the number 70 in C. The number
75 in D is 5 more than 70.

The same concept can be used to explain row 1 and 3.

Now look at column D.

15,45,75 .....

The sequence follows 15 + (n-1)15 where n is the number of row.

For 430 in C, the number in D will be 435.

435 ------ 15 + (n-1)15

This gives n ------29

Hence, Row 29 and Column C

Best wishes

[nounou]

This Q comes from St Hilda Prelim 2012 Q14. 2 marks. :yikes:

Zhu99:

ksme:

[quote=\"kuts\"]HI Ksme,

A B C D A A B B C C D D A A A B B B C C C D D D .....................? 160th

What is the 160th letter

Thanks in advance!


Hi,
Please see the solution below. It's not a very elegant way but it gives the answer in a reasonable time. By the way, where is this question from and how many marks is the question for?

Pattern :
ABCD ------------------- 4 (1 time each alphabet in a set of 4)
AABBCCDD---------------- 8 (2 times each alphabet in the set of 4)
AAABBBCCCDDD----------- 12 (3 times each alphabet in the set of 4)
AAAABBBBCCCCDDDD ------ 16 (4 times each alphabet in the set of 4)
etc ------ 20 (5 times each alphabet in the set of 4)
etc ------ 24 (6 times each alphabet in the set of 4)
etc ------ 28 (7 times each alphabet in the set of 4)
etc ------ 32 (8 times each alphabet in the set of 4)
etc ------ 36 (9 times each alphabet in the set of 4)

Adding the total number of alphabets for each set to come close to 160 letters = 4+8+12+16+20+24+28+32= 144.

The 160th letter is therefore belonging to the 9 times each alphabet set of 4.

160-144 = 16

Since A will be shown 9 times (16-9 = 7), therefore, the 160th letter will be B.

Hope the above helps.

A B C D --- 1 x 4
A A B B C C D D --- 2 x 4
A A A B B B C C C D D D --- 3 x 4

160/4 = 40 sets of 4

40 --- 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 4 [remainder of 4 sets]

4 x 4 = 16 letters left after (8 x 4) set

As next set is a set of 9, 16 - 9 (for 9 As) = 7 (the 7th B since it is less than 9).

The 160th letter is B.[/quote]

[nounou]

Wow wow wow!!! Uncle Tianzhu, you are super efficient!

:siam: 太厉害了！五体投地！ :thankyou: :udaman:

tianzhu:

Treelodge:

Please help. St Hilda Prelim 2012 Q5. 2 mark Q only. Why so difficult? Luan liao! :siao: :stupid: :xedfingers:
:thankyou: :thankyou: :thankyou: http://i50.tinypic.com/v3n22o.jpg\">

Hi

As seen from the table, numbers which are multiples of 10 are in column C.

Now study each row, take row 5.

The number 65 in B is 5 less than the number 70 in C. The number
75 in D is 5 more than 70.

Also 70 ------ ( 65+75)/2

The same concept can be used to explain row 1 and 3.

Now look at column D.

15,45,75

The sequence follows 15 + (n-1)15 where n is the number of row.

430 ------ 15 + (n-1)15

This gives n ------29

Hence, Row 29 and Column C

Best wishes

[Shimmer]

Hi I need help. Thanks


There are two bag of stones labeled A and B. In bag A ,there are 350 black stones and 500 white stones. In bag B , there are 400 black stone and 100 white stones. How many black and white should be transfer from bag B to bag A so that 50% of the stones in bag A and 75%of those in bag B are black?

[Michaelia0816]

Hi!

My teacher had assigned our math class’ pupils to do a question without using Guess and check. I stuck at the second step, my first step is 192cm-129cm=63cm.

When Mr Lim measured and recorded the height of these children, he wrongly recorded one child’s height as 192cm when it should have been 128cm.As a result, Mr Lim calculated the average height as 124.4cm. How many children were there in the group?

ASAP!