Question

下列哪个数的最大质因数最大？

Which of the following numbers has the largest prime factor?

$39$

$51$

$77$

$91$

$121$

把每个数完全分解成质因数

Factor each number completely into primes

比较每个分解式中的最大质数；注意 $51 = 3 \times 17$

Compare the largest prime in each factorization; note $51 = 3 \times 17$

分解得： $39 = 3 \times 13$ ， $51 = 3 \times 17$ ， $77 = 7 \times 11$ ， $91 = 7 \times 13$ ， $121 = 11 \times 11$ 。

这些最大质因数中最大的是 $17$ ，它是 $51$ 的因数。

所以正确答案是 B。

Factoring: $39 = 3 \times 13,$ $51 = 3 \times 17,$ $77 = 7 \times 11,$ $91 = 7 \times 13,$ and $121 = 11 \times 11.$

The largest prime factor among these is $17,$ which is a factor of $51.$

Thus, the correct answer is B .