Practice30Create account

Three adjacent angles lie along a straight line and their measures are in the ratio 3 : 5 : 4. Find the middle angle.

Class 7Lines and AnglesLines and Angles
  • A45°
  • B75°
  • C60°
  • D150°

Step-by-Step Solution

Angles on a straight line sum to 180°. The parts total 3 + 5 + 4 = 12, so one part = 180 ÷ 12 = 15°. The three angles are 45°, 75° and 60°, and the middle one is 5 parts = 75°. Trap: 150° comes from dividing 360° instead of 180° — a full turn is not a straight line.
Answer: B) 75°

Key idea: Linear pair

When two adjacent angles share a side, and their other sides together form a straight line, they make a **linear pair**. The two angles always sum to 180°.

If you know one of a linear pair, you can find the other by subtracting from 180°.

Master this chapter in 30 minutes a day.

Don't just memorise the answer — build a daily practice habit.

Practice 5 Similar Questions Free →

All Lines and Angles practice questions

More Class 7 Lines and Angles practice

Two straight lines cross at O. One pair of vertically opposite angles has a sum of 152°.…Ray OC lies between rays OA and OB, and ∠AOB is a straight angle. If ∠AOC is 5 times…Lines m and n are parallel and are cut by a transversal t. An angle at the…Lines p and q are parallel and are cut by a transversal. One interior angle at p…Can two right angles be supplementary to each other?