The natural logarithm of the activity \( R \) of a radioactive sample varies with time \( t \) as shown. At \( t = 0 \), there are \( N_0 \) undecayed nuclei. Then \( N_0 \) is equal to \([\text{Take} \ e^{7.5}] \)
From the given graph, we find the initial activity \( R_0 \) at \( t = 0 \) and its natural logarithm: \(\ \ \log_e R_0 = 7.5 \) Thus,\(\ R_0 = e^{7.5} \approx 75,000\)