If holly, alex and ben had 100 balls. holly had 20 balls and alex had 2x as many as she did, how many did ben have?

40 balls

Step-by-step explanation:

Let the number Ben has be A.

Holly, Alex and Ben had 100 balls.

Holly had 20

Alex had 2x holly = 2 x 20

= 40 balls

Therefore

20 + 40 + A = 100

60 + A = 100

Subtract 60 from both sides

60 - 60 + A = 100 - 60

A = 40

Ben had 40 balls

Check

Holly + Alex + ben

20 + 40 + 40

= 100 balls

Holly has 20 balls, and there are 100 balls in total.

So there are 100-20 = 80 balls left.

Alex had 2 * the amount Holly had, which is 20.

So Alex has 20 * 2 = 40 balls.

Together, they have 60 balls.

Which means 100-60 = 40. So Ben has 40 balls.

Check:

Holly: 20

Alex: 40

Ben: 40

Add them: 20 + 40 + 40 = 100