The population in 1950 was 1.7 million if that’s what you were asking
The total sum of students given four quarters = The student who spent the money on gum plus the students that kept the money.

The total sum of students given four quarters is 51 students.
The student who spent the money on gum is 34 students.
The probability of the students that spent the money, given that the students were given four quarters,

The probability is,

The probability is 0.667.
Im pretty sure it would be 4^-2 because when you’re multiplying two different exponents you add them. i hope i helped!