Whirlwind wrote:

It is taken from Bond Maths Assessment Papers Book 1, 10-11+ years.

The answer in the book must be a print error.

I have found this question in Maths Assessment Book 1, 10-11+, published 2014 - paper 12, q. 36-37.

In the same book published in 2007, paper 12, q. 36-37 the sequence is different, namely: 8, 8 1/2, 9 1/2, 11 1/2.

I have both sets of answers and in one of them the answer is given as 6 and 8 1/2 and the other one shows the answer as 15 1/5 and 23 1/5.

The odd thing is, that either I swapped the answer sections between the books or there was error somewhere in the BOND's bank of questions/answers and in both books incorrect answers were printed for this particular question (i.e. questions and answers got swapped by mistake).

15 1/2 and 23 1/2 are answers to the sequence 8, 8 1/2, 9 1/2, 11 1/2 (the differences between the terms are doubling, i.e. 8 plus 1/2, plus 1, plus 2, plus 4, plus 8 etc.)

The answers to the sequence 1, 1 1/2, 2 1/2, 4 are 6 and 8 1/2 ( the differences between the terms are 1/2, 1, 1 1/2, 2 etc).