You are asked about whether
k is a multiple of 40.This will be true if
k is divisible by 40.
Statement (1) tells you that
k is a multiple of 4. That means that
k could be, for instance, 8 or 80. 8 is not a multiple of 40 while 80 is a multiple of 40, so Statement (1) is not sufficient to answer the question in the stem.
Statement (2) tells you that
k is a multiple of 10. That means that
k could be, for instance, 20 or 80. 20 is not a multiple of 40 while 80 is a multiple of 40, so Statement (2) is not sufficient to answer the question in the stem.
Now combine the statements. This is the tricky part. You might have assumed that since 40 is the product of 4 and 10, that
k must be a multiple of 40. But again, try finding a number that is a multiple of both 4 and 10, but not of 40. In fact,
k could equal 20. So the statements, even when combined, are not sufficient to tell you whether
k is a multiple of 40 or not.
