Q&A - P5 Math

[tianzhu]

whywhy:

Hi Tianzhu, i need a simple method to do this St nick SA1 Q13.

Song Ren had a total of 50 coins. The coins were in denominations of 50ct, 20ct, & 5ct. He had an equal number of 50ct coins as 20ct coins. The total value of the 20ct coins & 5ct coins was $4.10. How many coins of each denomination did Song Ren have?

Hi

Good morning.

The total value of the 20ct coins & 5ct coins was $4.10.

$4 + 10 cents
$3.80 + 30 cents

Even value comes from the 20 cents coins and the odd amount from the 5 cents coins.

You may present your solution in a tabulated list similar to GC or “Assumption Method”. Try to establish a pattern.Here are some pointers.

$4 + 10 cents ------- 20 (20 cents coin) + 2 (5 cents coin) --------- 42 (20+20+2)

$3.80 + 30 cents ------- 19 (20 cents coin) + 6 (5 cents coin) --------- 44 (19+19+6)

Every increase of 20 cents (10 cents to 30 cents) leads to an increase of 2 coins (44-42)

50 - 42 ----- 8

8/2 ------ 4

Hence, we need 4 steps of an increase of 20 cents.

This gives 90 cents which is 18 number of 5 cents coin.

$3.20 + 90 cents ------ 16 (20 cents coin) + 18 (5 cents coin) --------- 50 (16+16+18)

5 cents ----- 18
20 cents ----- 16
50 cents ----- 16

Best wishes

[cimman]

whywhy:

Hi Tianzhu, i need a simple method to do this St nick SA1 Q13.

Song Ren had a total of 50 coins. The coins were in denominations of 50ct, 20ct, & 5ct. He had an equal number of 50ct coins as 20ct coins. The total value of the 20ct coins & 5ct coins was $4.10. How many coins of each denomination did Song Ren have?

this is one of those problem sums where algebra provides a simple solution.
http://i46.tinypic.com/2nbhwjl.png\">

[sherlynDD]

http://i47.tinypic.com/w05fzo.jpg\">


Can anyone help to solve? Thanks!

[tianzhu]

sherlynDD:

http://i47.tinypic.com/w05fzo.jpg\">


Can anyone help to solve? Thanks!

Hi

Where is this question from?

Slide triangle ABC until AT meets DV (no more overlapping)

Area of shaded area ------ 8*6 – (1/2*6*1.5) ------- 43.5

Another way

6*5 ------ 30

½*6*3 ------ 9

½*3*3 ------ 4.5

Total ------- 43.5

Best wishes

[sherlynDD]

tianzhu:

sherlynDD:

http://i47.tinypic.com/w05fzo.jpg\">


Can anyone help to solve? Thanks!

Hi

Where is this question from?

Slide triangle ABC until AT meets DV (no more overlapping)

Area of shaded area ------ 8*6 – (1/2*6*1.5) ------- 43.5

Another way

6*5 ------ 30

½*6*3 ------ 9

½*3*3 ------ 4.5

Total ------- 43.5

Best wishes

Hi tianzhu,

Thank you! This qn is from Nangyang CA2 2011.
The slide method is quite cool, but not easy to find out immediately.
The second way, I can not see how 6*5 come from. Thanks.

[tianzhu]

sherlynDD:

Best wishes

Hi tianzhu,

Thank you! This qn is from Nangyang CA2 2011.
The slide method is quite cool, but not easy to find out immediately.
The second way, I can not see how 6*5 come from. Thanks.[/quote]
Hi

You're welcome.

This is not an easy question for P5 kids.

8 - 3 ----- 5

From point S, extend a horizontal line to meet line DV, you'll see a rectangle of 6*5

Best wishes

[whywhy]

Thanks to Tianzhu. thanks to Cimman for the contribution. Is your algebra method taught in sch n acceptable by psle marker?

[despmom99]

whywhy:

Thanks to Tianzhu. thanks to Cimman for the contribution. Is your algebra method taught in sch n acceptable by psle marker?

Hi, whywhy

My child's tutor who is an ex-Math HOD is using this table method too. My child was revising the concept taught the other day. Think she gave a name to the concept. I check and let you know. I was quite concerned if this method was acceptable by psle marker and asked the tutor. She said yes. She was supervisor of some sort during the psle marking so I trust her.

[YumYum]

Hi, can anyone pls help with this Qn:


1. A seamstress had some white and black buttons. 60% of the buttons were white. She bought an additional 120 buttons. Now the percentage of white buttons became 40% of the total. How many white buttons did he have at first?


2. The ratio of the number of ten cent to twenty cent stamps in an album was 3:4. 50 ten-cent stamps were taken out, exchanged for twenty cent stamps of the same value and put back into the album. The ratio became 1:5. Find the total value of all the stamps in the album at first.

thanks

[tianzhu]

YumYum:

Hi, can anyone pls help with this Qn:


1. A seamstress had some white and black buttons. 60% of the buttons were white. She bought an additional 120 buttons. Now the percentage of white buttons became 40% of the total. How many white buttons did he have at first?

Hi

Q1 has been discussed before.

Please refer to page 209 of this thread.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=2080

Best wishes