MisterXYZ's answer to Fuzzy's Primary 5 Maths Percentage Singapore question.
done
{{ upvoteCount }} Upvotes
clear
{{ downvoteCount * -1 }} Downvotes
Another method that is different from the answe4 that was provided, But i hope this aids in your understanding.
Date Posted:
2 years ago
Your method , although arrives at the same final answer, is incorrect.
Notice that the perpendicular height of △APR is shorter than BQ (18cm), so to write △APR'S area as ½ × 12cm × 18cm is incorrect.
This means that area of PBQR is not 108cm²
The final answer was obtained correctly only because the two area PBQRs cancelled out when you did 108cm² - 36cm² = 72cm²
i.e
difference
= Area of △APR - Area of △RQC
= 108cm² - 36cm²
= (Area of △ABQ - Area of PBQR) - (Area of △PBC - Area of PBQR)
= (216cm² - 108cm²) - (144cm² - 108cm²)
= 216cm² - 108cm² - 144cm² + 108cm²
= 216cm² - 144cm²
= 72cm²
(216cm² - 144cm² would be the correct method which AC Lim used)
We could let area of PBQR be any value (eg. 50, 100,2) and you will still get the same difference of 72cm²
Notice that the perpendicular height of △APR is shorter than BQ (18cm), so to write △APR'S area as ½ × 12cm × 18cm is incorrect.
This means that area of PBQR is not 108cm²
The final answer was obtained correctly only because the two area PBQRs cancelled out when you did 108cm² - 36cm² = 72cm²
i.e
difference
= Area of △APR - Area of △RQC
= 108cm² - 36cm²
= (Area of △ABQ - Area of PBQR) - (Area of △PBC - Area of PBQR)
= (216cm² - 108cm²) - (144cm² - 108cm²)
= 216cm² - 108cm² - 144cm² + 108cm²
= 216cm² - 144cm²
= 72cm²
(216cm² - 144cm² would be the correct method which AC Lim used)
We could let area of PBQR be any value (eg. 50, 100,2) and you will still get the same difference of 72cm²
360 Tutoring Program