This doesn't seem possible to me. If I'm reading this correctly, a total of 400 mothers have babies with neural tube defects (0.04 x 10,000) but 2,000 mothers in the placebo group had babies with neural tube defects (0.4 x 5,000). Help!

For questions 17-20, use the following information. Alpha fetoprotein (AFP), a substance produced by a fetus, is often measured in pregnant women as a means of assessing whether there might be problems with fetal development. High levels of AFP have been seen in babies with neural-tube defects. A promising drug treatment is being studied to decrease AFP levels among pregnant mothers. A study consisted of 10,000 pregnant mothers were randomly assigned to either the drug treatment or a placebo group. These mothers were followed throughout the rest of their pregnancy. In the sample, 50% received the drug treatment, a total of 4% had babies born with neural-tube defects, and 60% of the pregnant mothers in the placebo group did not have a child born with a neural-tube defect. Note that you do not need to use probability for any part of this problem. Round your answers to the nearest whole number.

17.How many mothers had children born with a neural tube defect? (10,000)(0.04) = 400

18.How many mothers were in the placebo group? (10,000)(0.5) = 5,000

19.How many mothers in the placebo group had a child born with a neural-tube defect? (5,000)(1-0.6) = 2,000 <-- this doesn't make sense given the answer to #17 above.

20.How many mothers in the treatment group did not have a child born with a neural-tube defect? 400 total - mothers in placebo group = mothers in treatment group <-- this would be a negative number

Should I assume that 4% of the mothers who received the treatment had babies with neural tube defects? I can get the numbers to work that way. Thanks!