I think it's D - 35. I would set up a table for this type of problem and fill it out as you read through the question. The set up would be something like this:

______Size A_______Size B______Total
Red

Blue

Total


The first sentence allows us to fill in the last column with 75 and 25 and the second tells us the last row will be 50 and 50. Then, we are given 10 are in the upper left cell of the table (red and size A). Knowing this, we can fill in the upper right cell with 15 since the total number of red is 25. Similarly, we know that 40 must be blue and size A since the total number of size A must be 50. Finally, the # of blue and size B must be 35 so that the total # of blue is 75 and the total number of size B is 50.

The grid format would help you answer these questions.

Total Red toys - 25
Total blue toys - 75
Total Size A toys - 50
Total SIze B toys - 50
Red Size A toys - 10

SO Blue Size B toys can be derived as below;
Red Size A toys + Red Size B toys = 25
Substitute and u get the value of Red size B toys to b 15
Now, you can subbstitute similarly to get the value of Blue size B toys to be 35

To solve such issues, try using grids and it simplifies the problem.
Break down the given details into a grid reading Red, Blue and horizontal grids with the sizes.

Hope that helps.

Agree D

Guys thanks a lot. The correct answer is - D itself. Once again thanks a lot. But guys I would like to share something with you - Can you believe that I misunderstood the statement - "If 10 out of a lot of 100 toys are red and size A" to "If 10 out of a lot of 100 toys are red". And I got confused by that because in the question, one time it is saying that 25% of toys are red and in other time it is saying that 10 of 100 toys are red and I thought how it is possible! Guys can u pls tell me the way to avoid such type of carelessness and overlooking. Really looking for ur suggestion.

In each production lot for a certain toy, 25 percent of the toys are red and 75 percent of the toys are blue. Half the toys are size A and half are size B. If 10 out of a lot of 100 toys are red and size A, how many of the toys are blue and size B?
(A) 15
(B) 25
(C) 30
(D) 35
(E) 40

We are given that we have 100 toys, and we see that 50 are size A and 50 are size B.

We also see that 75 toys are blue and 25 are red.

Since 10 toys are red and size A, 50 - 10 = 40 are blue and size A.

Since 40 toys are blue and size A, 75 - 40 = 35 are blue and size B.

Answer: D