A tortoise is making its way to eat a piece of lettuce at a constant speed. On its way to the lettuce, it takes 10 seconds to walk past a grain of sand. It then passes a piece of wood 20 cm long in 30 seconds to get to the lettuce. What is the length of the tortoise?	Choose the correct choice from the following answers
A) 4 cm  B) 5 cm  C) 7.5 cm  D) 9 cm  E) 10 cm
Sol.
Let the length of the tortoise be x centimetres and its speed be y cm/sec. Then, x / y = 10 ⇒ y = x / 10
∴ (x + 20) / 30 = x / 10 ⇔ x = 10 cm. Answer 10 cm
<result>E</result>
A tortoise is making its way to eat a piece of lettuce at a constant speed. On its way to the lettuce, it takes 10 seconds to walk past a grain of sand. It then passes a piece of wood 20 cm long in 30 seconds to get to the lettuce. What is the length of the tortoise?