Question

A tortoise makes a journey in two parts; it can either walk at 4cm/s or crawl at 3cm/s. If the tottoise walks the first part and crawls the second, it takes 110 seconds. If it crawls the first part and walks the second, it takes 100 seconds. Find the lengths of the two parts of the journey.

Answer 1

120

240

Explanation:

We call the length of first part x

Length of second part = y

In the first scenario, it took the tortoise 110 sec to walk the first part and crawl the second.

So,

We have this equation,

x/4 + y/3 = 110

We take the LCM

(3x + 4y)/12 = 110

When we cross multiply

3x + 4y = 110x12

3x + 4y = 1320 ----- equation 1

For scenario 2

x/3 + y/4 = 100

When we take the LCM

(4x + 3y)/12 = 100

We cross multiply

4x + 3y = 100x12

4x + 3y = 1200 ------ equation 2

We now have two equations and we will solve for x and y using simultaneous linear equation.

3x + 4y = 1320 ----- 1

4x + 3y = 1200 ----- 2

We subtract equation 2 from 1 to get

- x + y = 120

We make y subject

y = x + 120 ----- 3

We put the value of y in equation 3 into equation 1

3x + 4(x + 120) = 1320

3x + 4x + 480 = 1320

7x + 480 = 1320

7x = 1320-480

7x = 840

We divide through by 7

x = 840/7

x = 120

We put value of x in equation 3

y = x + 120

y = 120 + 120

y = 240

120 and 240 are the lengths of the 2 parts of the journey.

Thanks