Math Riddles

Question: Man walks into a store and says to the shop owner: “I will spend $10 in your store if you double the amount of money I now have in my pocket.” Store owner agrees; doubles his money; he spends $10 and leaves. He repeats this at 2 more stores. When he leaves the 3rd store he has $0 dollars. How much money did he have in his pocket when he walked into the first store?

Question: 8,549,176,320 What makes this number unique?

Question: Hard, Harder, and Hardest are brothers. By age from youngest to oldest, it goes Hard, Harder, Hardest. Hard is half the age of Hardest who is 20 which means hard is 10. Harder has a two-year difference between the number of years older he is than Hard and the number of years younger he is than Hardest. Harder is closer to the age of Hard than Hardest. How old is Harder?

Question: Which is the missing number in the below Number Series? 2, 3, 5, 7, 11, 13, ?, 19

Question: How is 2+2 four, 3+3 eight, and 7+7 triangle?