If the thickness of a pile of 12 cardboard is 65 mm, find the thickness of a pile of 312 such cardboards.

More the no. of cardboards, more will be the thickness. So it is a direct proportion.

Let the thickness be x mm,

⇒ 12 × x = 65 × 312

⇒ x = = 1690 mm = 1m 690mm = 1m 69 cm