Let us draw a line XY parallel to ST and passing through point R.
\(∠\)PQR + \(∠\)QRX = 180º (Co-interior angles on the same side of transversal QR)
\(⇒\) 110º + \(∠\)QRX = 180º
\(⇒\) \(∠\)QRX = 70º
Also,
\(∠\)RST + \(∠\)SRY = 180º (Co-interior angles on the same side of transversal SR)
130º + \(∠\)SRY = 180º
\(∠\)SRY = 50º
XY is a straight line. RQ and RS stand on it.
∴ \(∠\)QRX + \(∠\)QRS +\(∠\)SRY = 180º
70º + \(∠\)QRS + 50º = 180º
\(∠\)QRS = 180º − 120º
= 60º
(Street Plan) : A city has two main roads which cross each other at the centre of the city. These two roads are along the North-South direction and East-West direction.
All the other streets of the city run parallel to these roads and are 200 m apart. There are 5 streets in each direction. Using 1cm = 200 m, draw a model of the city on your notebook. Represent the roads/streets by single lines. There are many cross- streets in your model. A particular cross-street is made by two streets, one running in the North - South direction and another in the East - West direction. Each cross street is referred to in the following manner : If the 2nd street running in the North - South direction and 5th in the East - West direction meet at some crossing, then we will call this cross-street (2, 5). Using this convention, find:
(i) how many cross - streets can be referred to as (4, 3).
(ii) how many cross - streets can be referred to as (3, 4).