60% of customers pay for their meals with a credit card. What fraction of customers did not use credit cards?

Answer:I think it is 2/5

40% = 4/10 = 2/5

We can easily see that 60% + 40% = 100

But in calculi we could always show

x=10

6x + 4x = 10x

10x - 4x = 6x

10x - 6x = 4x

When we add them together

we find 20

20/4 = square of 4 + 4/5

20 + 4 / 2 x 3 = square of 6

x (x - 4) = x^2 - 4x

and we see the customers use credit above, where concerned the customers don't use credit we can show

x (x - 6)

x^2 - 6x

10^2 - 6x

100 - 60

=40

=4/10

=2/5