Question: Maths Year 5
DRILL & PRACTICE
PRACTICE 2 Find the unknown angles marked with ‘y’. Show your working steps in the spaces provided.
(1)
156°
y
(2)
168°
171°
y
(3)
30°
46°
107°
y
(4)
y
60°
20°
1. **Problem:** Find the unknown angle $y$ when the other angle is $156^\circ$ and both angles form a straight line.
2. **Formula:** Angles on a straight line sum to $180^\circ$.
3. **Calculation:**
$$y + 156 = 180$$
$$y = 180 - 156$$
$$y = 24^\circ$$
---
1. **Problem:** Find the unknown angle $y$ when the other two angles are $168^\circ$ and $171^\circ$ around a point.
2. **Formula:** Angles around a point sum to $360^\circ$.
3. **Calculation:**
$$y + 168 + 171 = 360$$
$$y + \cancel{(168 + 171)} = 360$$
$$y + 339 = 360$$
$$y = 360 - 339$$
$$y = 21^\circ$$
---
1. **Problem:** Find the unknown angle $y$ when the other three angles are $30^\circ$, $46^\circ$, and $107^\circ$ around a point.
2. **Formula:** Angles around a point sum to $360^\circ$.
3. **Calculation:**
$$y + 30 + 46 + 107 = 360$$
$$y + \cancel{(30 + 46 + 107)} = 360$$
$$y + 183 = 360$$
$$y = 360 - 183$$
$$y = 177^\circ$$
---
1. **Problem:** Find the unknown angle $y$ when the other two angles are $60^\circ$ and $20^\circ$ around a point.
2. **Formula:** Angles around a point sum to $360^\circ$.
3. **Calculation:**
$$y + 60 + 20 = 360$$
$$y + \cancel{(60 + 20)} = 360$$
$$y + 80 = 360$$
$$y = 360 - 80$$
$$y = 280^\circ$$