$\displaystyle \frac{12}{15} = \frac{12 \div 3}{15 \div 3} = \frac{4}{5}$, so $\displaystyle 6\frac{12}{15}$ simplifies to $\displaystyle 6\frac{4}{5}$.

The numerator of the improper form of a mixed fraction is the original numerator added to the product of the integer and the original denominator. The new denominator is the same as the old one. Therefore, 

$\displaystyle 6\frac{4}{5} = \frac{6 \times 5 + 4}{5} = \frac{30+4}{5} = \frac{34}{5}$ 

Multiply the numerator and the denominator: $\displaystyle 34 \times 5 = 170$,

a three-digit number.

$\displaystyle \frac{16}{60} = \frac{16 \div 4}{60 \div 4} = \frac{4}{15}$

Add the numerator and the denominator: $\displaystyle 4+15= 19$

The correct response is therefore $\displaystyle 15 < N \le 20$.

The prime factorization of $\displaystyle 65$ is $\displaystyle 5 \times 13$, so the fraction $\displaystyle \frac{N}{65}$ is reducible if and only if $\displaystyle N$ is a multiple of 5 or 13.

We can immediately tell that 115 is the only multiple of 5, so we test the other numbers to see if there is a multiple of 13. We soon see that

$\displaystyle 117 \div 13 = 9$, so 116 and 118 cannot be multples of 13.

115 and 117 are the only values of $\displaystyle N$ that yield reducible fractions, so the correct response is two.

$\displaystyle \frac{39 \div 3}{111 \div 3} = \frac{13}{37}$

Multiply the numerator and the denominator: $\displaystyle 13 \times 37 = 481$

The product is a three-digit number.

To put a fraction in simplest form, keep dividing the numerator and denominator by the same number until you cannot go any further.

$\displaystyle \frac{24\div2}{36\div2}=\frac{12}{18}$

$\displaystyle \frac{12\div2}{18\div2}=\frac{6}{9}$

$\displaystyle \frac{6\div3}{9\div3}=\frac{2}{3}$

To simplify a fraction, divide both the numerator and the denominator by the same numbers until there is no number that can divide them both without resulting in a remainder.

$\displaystyle \frac{224\div4}{400\div4}=\frac{56\div2}{100\div2}=\frac{28\div2}{50\div2}=\frac{14}{25}$

To simplify a fraction, divide both the numerator and the denominator by the same numbers until there is no number that can divide them both without resulting in a remainder.

$\displaystyle \frac{36 \div 12}{120 \div 12}=\frac{3}{10}$

To simplify a fraction, divide both the numerator and the denominator by the same numbers until there is no number that can divide them both without resulting in a remainder.

$\displaystyle \frac{48\div12}{120\div12}=\frac{4\div2}{10\div2}=\frac{2}{5}$

To simplify a fraction, divide both the numerator and the denominator by the same numbers until there is no number that can divide them both without resulting in a remainder.

$\displaystyle \frac{20\div4}{36\div4}=\frac{5}{9}$

To simplify a fraction, divide both the numerator and the denominator by the same numbers until there is no number that can divide them both without resulting in a remainder.

$\displaystyle \frac{24\div4}{100\div4}=\frac{6}{25}$