Q&A - P5 Math

[Chan09]

Couldn’t figure this one: what is the greatest number of right angles that a 5 sided figure can have? Ans: 4

I couldn’t draw the figure? Thanks

[tianzhu]

Chan09:

Couldn't figure this one: what is the greatest number of right angles that a 5 sided figure can have? Ans: 4

I couldn't draw the figure? Thanks

Hi

Just throwing up some thoughts, I am not sure if we can count the right angles formed by adjacent perpendicular lines.

Best wishes.

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[linden2000]

Hi. Just my thoughts below:


Sum of interior angles of n-sided polygon is (n-2) x 180 degrees
so sum of interior angles of 5-sided figure = (5-2) x 180 = 540 degrees

If max no. of right angles is 4, that will mean the remaining last angle is
540 - 4x90 = 180 degrees

That’s only possible if you allow for collinear vertices, ie vertices that lie in
same straight line. But that will mean a 4-sided figure is the same as a 5-sided figure.

Else if no collinear vertices allowed, would think max no. of right angles is 3.

[Chan09]

Tks as felt question was a bit misleading.

[Jcong]

Pail A contained 7/17 of the amount of water in Pail B. Pail C contained 1/9 of the total amount of water the three pails had. If Pail A and Pail B contained 5.25 litres of water more than Pail C, how much water did Pail B contain? (give the answer in litres)

[tianzhu]

Jcong:

Pail A contained 7/17 of the amount of water in Pail B. Pail C contained 1/9 of the total amount of water the three pails had. If Pail A and Pail B contained 5.25 litres of water more than Pail C, how much water did Pail B contain? (give the answer in litres)

Hi

Pail A ----- 7 units

Pail B ----- 17 units

Multiples of 9 ------- 9, 18,27 ………

1/9*27 -----3 units

Pail C ------ 3 units.

24units – 3 units ------ 21units

21units ----- 5.25

1unit ----- 0.25

Pail B -----17*0.25 ------- 4.25

Best wishes

[Jcong]

Why do you use multiple of 9? and why is 27 chosen instead of other numbers like 18? So sorry don’t really understand. Thanks

[tianzhu]

Jcong:

Why do you use multiple of 9? and why is 27 chosen instead of other numbers like 18? So sorry don't really understand. Thanks

Hi

C contained 1/9 of the total amount of water the three pails had.
Hence, we use multiples of 9, just to make the calculations easier.

The number of units for Pail A and Pail B add up to 24(7+17).

Hence the total number of units(A+B+C) has to be greater than 24.

Alternatively, you may use MD.

7units (Pail A) +17units (Pail B) + 1part (Pail C) ------- 9 parts (representing A+B+C)

24units ------- 8parts

3units ------- 1part.

Best wishes

[Jcong]

Thank you so much. Now I understand.

[tianzhu]

Jcong:

Thank you so much. Now I understand.

Hi

Good Morning.

You’re welcome.

Best wishes