Well, you can help a lot of people if you get it wrong, too. There's two axes - helping a number of people and how much help each one receives. For example, you can buy half a million albuterol canisters in Kenya and alleviate asthma symptoms for a month; you can adopt a single mother, hire a home assistant for her, send all three of them to school, and that's a lot of help but for not many people.
Education. Health. Housing. You can spend a boatload of money in every category.