The blog postings are about the Singapore Math. The readers can learn from the postings about Solving Singapore Primary School Mathematics. The blog presents the Math Concept, Math Questions with solutions that teaches in Singapore Primary Schools. You or the kids can aquire the skills of dealing with Math Modeling, Math Problem Solving and Problem Sum from Lower Primary School to Upper Primary School level after reading the blog postings. This posting is an upper primary school math question on Lines and Angles.

Read the posting on **Sarin learns Lines and Angles (Math concept)** to understand the concept of lines and angles.

*Challenge yourself with the question before look out for the given solution‼!*

**Upper primary school mathematics question UPQ385**

In the figure below, XU, WZ, YO and VO are straight lines. ∠ YOX = ∠ VOW = 90°. If ∠a + ∠ c = 90^{0}. Find ∠ d.

*Solution:*

∠ YOX = 90^{0} and XU is a straight line,^{ }

∠ a + ∠ b = 90^{0}

∠ VOW = 90^{0} and WZ is a straight line,

∠ b + ∠ c = 90^{0}

∠ a + ∠ b + ∠ b + ∠ c = 90^{0} + 90^{0}

∠ a + ∠ c + 2 ∠ b = 180^{0}

Since ∠ a + ∠ c = 90^{0}

90^{0 }+ 2 ∠ b = 180^{0}

2 ∠ b = 90^{0} = 45^{0} + 45^{0}

∠ b = 45^{0}

XU and WZ are straight line,

∠ d = ∠ b = 45^{0}

To note: Only ∠ a = ∠ b = ∠ c = ∠ d = 45^{0}, then ∠ a + ∠ c = 90^{0} in this case.