Q&A - PSLE Math

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


6)\tLucas drank 45% of a bottle of pepsi. If he drank another 1 35m1, he would have drank 75% of it. How much pepsi was there in the bottle at first?

75% - 45% = 30%
30% --> 135 ml
100% --> 450 ml

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


8)\tAnne, Ben and Chris shared the cost of their seafood dinner. Anne paid 40% the total amount and Ben paid 30% of what Anne and Chris paid. If Ben paid $36 less than Chris, how much did Anne pay?

Amount paid by
Ben: Anne + Chris = 3:10 --> Ben : Anne+Ben+Chris = 3 : 13 --> 30u : 130u

Amount paid by
Anne : Anne+Ben+Chris = 4 : 10 -->52u : 130u

Amount paid by Chris --> 130u - 30u - 52u = 48u

Ben paid $36 less than Chris, so
48u-30u = 18u --> $36
1u --> $2

Anne paid --> 52 x $2 = $104

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


7)\tMr Low had 40% more cows than sheep. After he sold 375 cows and bought 375 sheep, he had 80% lesser cows than sheep. How many sheep did he have in the end?

Total number of cows and sheep remain the same.
At first, cows : sheep = 140 : 100 --> 7u : 5u
In the end, cows : sheep = 20 : 100 --> 2u : 10u
7u-2u = 5u --> 375
1u --> 75
Number of sheep in the end --> 750

cheers.

[jewelbox]

Hi, how do i solve this qn. My ans of 500 is wrong. Ans given is 494.4 min. Thanks. http://i45.tinypic.com/2ykjfcw.jpg\">

[zombie]

wow ! thanks a lot. I ‘ve waited for many days for the answers.


My mom told me that this website is for those who are already very good at maths, and that my questions are not challenging enough for you guys to help. But you all prove her wrong !

my maths is just mediocre.
ooh I’m so happy. . . . and my mom is getting me a tutor thru this website too. he is coming to teach me in 2 days’ time.

[susutoo]

MathIzzzFun:

susutoo:

hi,

sorry forget to attached image
http://i45.tinypic.com/nqusdd.jpg\">

alternate approach :

fill in the unshaded with the area of quadrants and semi circle
--> 3/4 x 22/7 x7 x7 = 115.5 cm2

Total area of the rectangle = 115.5 + 91.5 = 207 cm2

The breadth and length of the card are whole numbers
--> 207 = 23 x 9

perimeter of rectangular card = (23+9) x 2 = 64 cm

cheers.

Thanks MathIzzzFun and trytry :salute:

[Spongy]

Please help me in some questions. Thanks in advance!!!


1. A box contains 40 similar writing pads. The total mass of box with 3/5 of its contents is 0.88kg lighter than the box with all its contents. The mass of each writing pad is 4/5 times the mass of the box. Find the total mass of the box of writing pads. Give your answer in grams.

2. A train, 135m long travels at a constant speed of 15m/s. The train entered a tunnel which 4365m long at 12pm. Point B is the end of the tunnel.
(a) What time will it be for the entire train pass through the tunnel?
(b)What is the distance from point B to the next station if the train reaches the next station at 12.12pm.

3. In the figure below, not drawn to scale, triangle ABG is a right-angled triangle. Find angle BAC.
http://i46.tinypic.com/xmr312.png\">

[MathIzzzFun]

jewelbox:

Hi, how do i solve this qn. My ans of 500 is wrong. Ans given is 494.4 min. Thanks. http://i45.tinypic.com/2ykjfcw.jpg\">

For every min, the increase in water level when Tap A is filling
--> 5000/(250x40) = 0.5 cm
For every min, the decrease in water level when Tap B is draining
--> 2000/(250x40) = 0.2cm

For every 3 min Tap A is filling, increase in water --> 3 x 0.5 = 1.5 cm

For every 6 min ie every 3 min Tap A is turned on and every 3 min Tap B is turned on, increase in water level
--> (0.5-0.2) x 3 = 0.9 cm

3/4 of tank to be filled --> 3/4 x 100 cm = 75 cm of water

Assuming that Tap A will fill the tank to brim in the last 3 min,
(75-1.5)/0.9 = 81 2/3 --> round to 82
82 x 6 min = 492 min
After 492 min, water level in tank will be = 82 x 0.9 cm = 73.8 cm
75 cm-73.8 cm = 1.2 cm ---> 1.2 cm more to fill by Tap A
1.2/0.5 = 2.4 min

Total time to fill tank to brim without overflowing
= 492 min + 2.4 min= 494.4 min

cheers.

[dicoyote]

Hi,


Need help on these question:

1) Chris and Diane have some carnival tickets. If Chris sells 10 tickets per day and Diane sells 5 tickets per day. Chris will have 40 tickets left when Diane has sold all her tickets. If Chris sells 5 tickets per day and Diane sells 10 tickets per day, Chris will have 70 tickets left when Diane has sold all her tickets.
a) How many tickets does Chris have?
b) If each ticket is sold for $20, how much money can be collected from the sale of all their tickets?

For (a), I am trying to use algebra, but could not figure out after having the days as "x"

10x+40=5x
5x+70=10x…is this correct?

2) The ratio of the number of apples to the number of oranges in Box A is 4:1 while that in Box B is 3:2. Box A has thrice as many fruits as Box B. When 14 oranges are transferred from Box A to Box B, the number of oranges in Box A is 7/8 of the number of oranges in Box B. Find the number of apples in Box A at first.

Thanks in advance

[MathIzzzFun]

Spongy:

Please help me in some questions. Thanks in advance!!!



3. In the figure below, not drawn to scale, triangle ABG is a right-angled triangle. Find angle BAC.
http://i46.tinypic.com/xmr312.png\">

http://i47.tinypic.com/10nvr7b.png\">

angle EGF --> 1 unit
angle EFD --> 2 units
angle DEC --> 3 units
angle CDB --> 4 units
angle BCA --> 5 units
anlge BAC --> 5 units
angle EGF + angle BAC = 6 units --> 90 deg
1 unit --> 15 deg
angle BAC --> 75 deg

cheers.