Our galaxy, the Milky Way, has somewhere between 100 billion and 400 billion stars (it's difficult to estimate precisely). However, it's not really "typical"; it has more stars than any other galaxy in the "Local Group" except for the Andromeda Galaxy, which has about a trillion stars. I'm not sure there really is such a thing as a "typical" galaxy.
The number of stars in a galaxy can be estimated by measuring the total amount of light in the galaxy and knowing the mass distribution of the stars. It is estimated that there are roughly 100 billion stars in the Milky Way galaxy.
No. A typical galaxy has billions of stars.
they estimate how many stars the galaxy has: by measuring the size and brightness of the galaxy
Many estimates in astronomy have some uncertainty to them, and the estimate of the number of stars in our galaxy is no exception. Even the world's largest telescopes can't count the stars. They see only the brightest and nearest stars - and stars not obscured by dust. To estimate the number of the Milky Way's stars, astronomers first assume there's nothing special about our region of space. They determine the number of different types stars in this region - then extend this knowledge to the galaxy as a whole. The most popular current models suggest the Milky Way is about 100,000 light-years across. The estimate for the number of stars is about 100 billion stars - plus or minus 50 billion.
Groups of stars, such as clusters or galaxies. A typical galaxy can have hundreds of billions of stars. Also, quasars - as bright as a hundred typical galaxies.
They make reasonable estimates, based on the number of galaxies, and the size of a typical galaxy.
It is hard to say what is "typical", since galaxies vary quite a lot in size. Our galaxy has between 100 and 400 billion stars; some other galaxies are larger, but there are also lots of dwarf galaxies, some of which have only a few million stars. A typical spiral galaxy, like ours, has a few hundred billion stars.
The average number of stars in a dwarf galaxy is several billion.
This varies extremely from galaxy to galaxy, from tiny galaxies with 10 million stars, to huge ones with 1000 billion stars. The average is somewhere between 100 and 1000 billions. An exact number is hard to give, as we don't even know the number of stars in our own galaxy (between 100 and 400 billions). And there are 170 billion galaxies in the observable universe, so counting the average number of stars could take a while
The average number of stars in a giant galaxy since it contains trillions of stars is 10 trillion.
One way to increase the number of stars in a galaxy is for the two galaxies to collide.