Of the 100 soccer balls that Nova went to inflate, 40 percent had holes in them and could not inflate, while 20% of the remaining balls were overinflated and exploded. How many balls were inflated successfully and could be used?
Let's think: If 40% of the balls had holes in them and could not inflate, their number was 40 / 100 * 100 = 40. The remaining balls that Nova could inflate were 100 - 40 = 60. While inflating, 20% of the good soccer balls were overinflated and exploded up, a total of 20 / 100 * 60 = 12. The number of soccer balls that inflated successfully and could be used is 60 - 12 = 48.. The answer is: 48.

If you double a number and add 5 to the result, then that's 20 more than half of the original number. What's the original number?
Let's think: Let x be the original number. 2 * x + 5 = 20 + x / 2. 2 * x - x / 2 = 15. 4 * x - x = 30. 3 * x = 30. x = 10.. The answer is: 4.

In four years, Suzy will be twice Mary's age then. If Suzy is 20 now, how old is Mary?
Let's think: In four years, Suzy will be 20 + 4 = 24. Then Mary will be 24 / 2 = 12. Then Mary is now 12 - 4 = 8.. The answer is: 8.

Hannah sold 40 pieces of cookies for $0.8 each and 30 cupcakes for $2 each. She used the money to buy 2 sets of measuring spoons for $6.5 each. How much money does she have left?
Let's think:
Hannah's earnings from the cookies is 40 x $0.8 = $32. Her earnings from the cupcakes is 30 x $2 = $60. Her total earnings for the cupcakes and cookies is $32 + $60 = $92. The cost of 2 sets of measuring spoons is 2 x $6.5 = $13. So, Hannah has $92 - $13 = $79.. The answer is: 79.