Answer:
There were 120 marbles to start
Explanation:
Let x be the number of marbles at the start
x* 5/12 = number of marbles given away
1 -5/12 = 7/12 = fraction of marbles left
x * 7/12 = number of marbles left
x * 7/12 = 70
Multiply each side by 12/7
x *7/12 * 12/7 = 70 * 12/7
x =120
There were 120 marbles to start