There are 24 people using the gym. the ratio of men to women is 2: 1

People using the gym = 24
ratio of men to women = 2:1
it means women are 2 times more than men.
let x be the number of men than:
2x+x = 24
3x = 24
x = 8
so, the number of men in the gym is 8 and number of women in the gym is 16.

Let the number of women using the gym be y
since the number of men using the gym is twice the number of women
(ratio is 2:1), therefore:
number of men using the gym is 2y

The total number of people using the gym is 24. Therefore:
y + 2y = 24
3y = 24
y = 24/3 = 8

Therefore:
number of women using the gym = 8 women
number of men using the gym = 2 x 8 = 16 men