Mary wants to ride the world's tallest roller coaster, Kingda Ka. The minimum height to ride the roller coaster is 140 cm. Mary's brother is 180 cm, Mary is 2/3 the height of her brother. How many more centimeters does Mary need to grow to ride Kingda Ka? Let's think first. Chain of thought:
Being 2 / 3 of her brother's height, Mary is 180 * 2 / 3 = 120 cm. To reach the minimum height and ride Kingda Ka, Mery needs to grow 140 - 120 = 20 cm.
Therefore, the answer is 20.