Rebecca went swimming yesterday. After a while she had covered one fifth of her intended distance. After swimming six more lengths of the pool, she had covered one quarter of her intended distance. How many lengths of the pool did she intend to complete?

E. 120

Step-by-step explanation:

A. 40

B. 72

C. 80

D. 100

E. 120

Let

x = the intended distance

y = length of the pool

She covers one fifth of her intended distance

Distance covered = 1/5 of x

= x/5

After swimming six more lengths of the pool she had covered one quarter of her intended distance

x/5 + 6y = 1/4 of x

x/5 + 6y = x/4

Collect like terms

6y = x/4 - x/5

6y = 5x - 4x/20

6y = x/20

x = 20 * 6y

= 120y

x = 120y

The intended distance Rebecca wants to cover = 120