Question

A machine part is drawn two times with different scales. The ratio of 1st drawing’s R.F. to 2nd drawing R.F. with respect to the actual object is found to be 2. The length of the second drawing is 10 mm. Find the 1st drawing length.

(a) 5 mm

(b) 200 mm

(c) 5 cm

(d) 2 cm

This question was posed to me in semester exam.

My doubt is from Representative Factor topic in division Scales of Engineering Drawing

Answer 1

Right choice is (d) 2 cm

To elaborate: 2 = 1st drawing R.F/2nd drawing R.F. = (length of 1st drawing/actual length)/(length of 2nd drawing/ actual length) = length of first drawing/length of second drawing = length of first drawing/ 10 mm. 2 x 10 mm = 20 mm. So therefore the length of first drawing is 20 mm = 2 cm.