Ask Singapore Homework?

Upload a photo of a Singapore homework and someone will email you the solution for free.



Question

primary 5 | Maths | Area & Volume
One Answer Below

Anyone can contribute an answer, even non-tutors.

Answer This Question
Kc
Kc

primary 5 chevron_right Maths chevron_right Area & Volume chevron_right Singapore

Please help. Thanks

Date Posted: 4 years ago
Views: 304
snell
Snell
4 years ago
area ABC = 0.5 x 20 x 12 = 120 cm²

area BDC = 0.5 x 5 x 12 = 30 cm²

area ADC = 120 - 30 = 90 cm²
J
J
4 years ago
As assumption has to be made here, that the unshaded triangle is a right angled one.

See 1 Answer

done {{ upvoteCount }} Upvotes
clear {{ downvoteCount * -1 }} Downvotes
AC Lim
Ac Lim's answer
12008 answers (A Helpful Person)
1st
Actually triangle with dimensions 5cm, 12 cm and 13 cm is right angle triangle. .. but primary level haven’t teach. Hope this helps
J
J
4 years ago
This diagram is mathematically incorrect as the unshaded triangle is supposed be right angled as well, but its dimensions don't satisfy the Pythagoras' theorem since 15² + 12² = 369 ≠ 20²
snell
Snell
4 years ago
still make use of info that angle ADC is right angle
J
J
4 years ago
To be fair to a P5 student, the value of angle BDC and ADC aren't even given. Amd neither are stated as right angles.

Hence my earlier comment that it has to be assumed that BDC is right angled (which then would imply that ADC is right angled since AB is taken to be a straight line), since they're not expected to infer that the shaded triangle satisfies Pythagoras' Theorem and thus conclude BDC is 90°.

Or, assume that ADC is right angled.
AC Lim
AC Lim
4 years ago
How about use AD : BD = 3:1... are we able to find area for ABC... ?
J
J
4 years ago
Will still get 120 cm² for ABC
AC Lim
AC Lim
4 years ago
Meaning we still need to assume ADC is a right angle.Really mathematically error question;(
J
J
4 years ago
Yup. The teacher/set probably expects assumption to be done. Otherwise it could be that they forgot to mark either as a right angle.
J
J
4 years ago
If we let AC = AB be x instead,

Then x² = 12² + (x - 5)²

x² = 144 + x² - 10x + 25

10x = 169
x = 16.9

So what the teacher/setter should have done is let AB = AC = 16.9 cm