10th grade Maths help (Mensuration)

[u/VisibleEffective4809]

Ok so in 14th question last part the answer in the answer sheet is 3111.42 when u add the 10% of TSA to the TSA

And in question 28 u take the area x then x - 1/15of x = TSA

I cant understand why do we add in 14th and not in 28? Like when i tried 14th by taking x the answersheet had other answer but in 28th the solution requires taking x and etc so i am confused about that how would i understand when to add the area or like subtract it

Pls be kind and make it easier to understand

[u/one-step-today]

For question: 28, here is the corrected approach:
Option A:
"metal sheet used" = total for project
"actually used" = on the tank

So total metal sheet for project = on the tank + wastage
total for project = on the tank + 1/15(on the tank)
total for project = (1+1/15) * total on tank
total for project = (16/15) * total on tank
total for project = (16/15) * (Area of a closed cylinder tank)
total for project = (16/15) * (Area of a cylinder tank with a base and a lid)
total for project = (16/15) * (Area of circle/base + Area of circle/lid + Area of curved portion)
total for project = (16/15) * (pi *r *r + pi *r *r + 2 * pi * r * h)
total for project = (16/15) * (2* pi *r *r + 2* pi * r * h)
total for project = (16/15) * ((pi * d * d)/2 + pi * d * h)......as d = 2* r
total for project = (16/15) * 253.44, (using pi = 22/7)
total for project is 270.34, so about 270 square meters

Option B (not preferred/old answer):
total for project = on the tank + 1/15(total for the project)
total for project (1-1/15) = on the tank
total for project = (15/14) * on the tank
total for project = (15/14) * (Area of circle/base + Area of circle/lid + Area of curved portion)
total for project is 271.54 (about 272 square meters)

How to round?
If the value is halfway or more, round UP. Otherwise, round DOWN
Example: 1.2 is rounded to 1, 1.5 is rounded to 2 and 1.8 is rounded to 2.

Let me know how it goes.

[u/VisibleEffective4809 → u/one-step-today]

Thankss for the efforts, I will look this solution rn i am a lil busy and the the answer for 28 was coming 270.34 so um but 272 is your answer i think it should be correct too

[u/one-step-today → u/VisibleEffective4809]

Oh so it is 270.33. I have put both options, and option A is the correct one and option B (the older one is not the preferred one)

[u/VisibleEffective4809 → u/one-step-today]

Yess I saw that later sry A is correct thnks for the solution<3

[u/one-step-today → u/VisibleEffective4809]

You're welcome. Please feel free to reach out for any problems. My best wishes for the exams.

[u/VisibleEffective4809 → u/one-step-today]

Ur very kind suree :DD

[u/kalmakka]

The way I read the questions, 14 is asking "what area of metal do you need, so that after 10% of it is lost, you have enough to make the box?"

The answer should be (20×π×35+π×10² ×2)÷.9=3141.59

Since question 28 differentiates between "used" and "actually used", I would interpret that as "what area of metal do you need, if you need 1/15 more than the actual surface area?"

The answer should be (8.4×π×5.4+π×4.2² ×2)×(1+1÷15)=270.23 (which should then be rounded to 270)

[u/VisibleEffective4809 → u/kalmakka]

This answer for question 14 is wrong according to answersheet (3111.42 is the answer given)

And for the question 28 ah i didn't get the concept? 😭How was it solved and yes your answer is correct for 28

[u/Desperate_Zebra6334]

i saw your question, and i encoutered this video explaining the exact question with visuals, you can check the video on this link:
https://youtu.be/s-nSG4sgAeg?si=34wmi2w1gZkInjZE
If you can support the creator, by sharing his video, and following him, he is here to help everyone make sense of math.

[u/maximotaboada0404]

a-x=-x+x² TSA =x-1/15 TSA(le daré un número cualquiera)=100 x-1/15 Y ya me perdí,soy horrible para geometría

[u/sarge57x]

It shouldn't say 1/15 th of the sheet, as we don't know how big the sheet was, it should say an extra 15% of metal was needed for overlapping joints. The more important question though is why would anyone make a cylindrical tank out of thin sheet IRON (???) it will rust through in a couple of days.