You are correct finance lady. Wash sales loss is not allowed maybe what is tricking you is that they did not buy the entire 500 shares within 30 days. They only bought 250. So from the 1000 loss only 500 is dissalowed. The new shares basis needs to include the dissalowed loss. like this:
P 500 * 25
S 500 * 23
Loss of 1000
P 250 * 25
S 100 * 18
The basis of the new 250 shares is increased by the dissalowed loss: 500/250 = 2
25+ 2 = 27 (which to match AICPA answer the 250 should be 22 per share not 25 maybe its a typo)
therefore
P 250 * 24
S 100 * 18
Loss 600
Allowed first loss 500 + 600 second loss = 1,100
but if indeed the number of shares for teh second purchaes was 250 at 25 per share then it should have been D.
P 250 * (25 + 2)
S 100 * 18
Loss 500 allowed + 900 = 1400
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