Estimation Station 3 - How many rubberbands will it take to make the watermelon explode?

"It won't work."
"How many rubberbands are in the bowl?"  (Answer: 700)
"Can I touch the rubberbands?"  (Yes) "Oh, they are strong."
"Do you know the answer?"  (No)
"Are you going to do it?" (Yes at 3rd lunch at 11:45)
"I got it. I know I am right."

How many do you think?