To find how many times greater the number of bacteria in petri dish A is compared to petri dish B, we divide the number of bacteria in petri dish A by the number of bacteria in petri dish B.
Let:
- \( A = 1.75 \times 10^{18} \) (bacteria in dish A)
- \( B = 6.25 \times 10^{15} \) (bacteria in dish B)
Now, calculate the ratio:
\[ \frac{A}{B} = \frac{1.75 \times 10^{18}}{6.25 \times 10^{15}} \]
We can simplify this expression:
\[ \frac{A}{B} = \frac{1.75}{6.25} \times \frac{10^{18}}{10^{15}} = \frac{1.75}{6.25} \times 10^{18 - 15} = \frac{1.75}{6.25} \times 10^{3} \]
Now, calculate \( \frac{1.75}{6.25} \):
\[ \frac{1.75}{6.25} = 0.28 \]
Thus, we have:
\[ \frac{A}{B} = 0.28 \times 10^{3} \]
Converting \( 0.28 \times 10^{3} \) into standard notation:
\[ 0.28 \times 10^{3} = 2.8 \times 10^{2} \]
Therefore, the number of bacteria in petri dish A is \( 2.8 \times 10^{2} \) times greater than that in petri dish B.
The final answer is:
\[ \boxed{2.8 \times 10^{2}} \]