23) D

Let us look at the left hand side first.
So far, the left hand side adds up to 8. It needs 13 more to make 21. The 13 can only be made up of 6 and 7. We do not know which order though.

On the right side, we have a total of 11. It needs 10 more to become 21. The 10 cannot be made from  6 and 4 since 6 is needed on the left hand side.

If we put 6 at the top left, we get a total of 15 on the top row. 6 more is needed. Since 6 is needed, 8 cannot be on the top right. Hence, 2 will be at the top right.
So far, we have 6 + 9 + 2 = 17 on the top row. If we put 4 on the third house on the top row, we can get 21.

If we put 7 above the 3 on the left hand side, we get:
6 + 5 + 7 + 3 = 21

If we put 8 on the bottom left, below the 1, we get:
2 + 10 + 1 + 8 = 21

Hence, between 3 and 5, number 7 is present.

## 2 thoughts on “2011 Section 1 Question 23”

1. A says:

In the second sentence it is supposed to be 8 instead of 18. 5+3 = 8. Although explanation is correct.

1. Hi, thank you so much for pointing that out! I’ve corrected it now.

Manas