Question

What will come in place of the question mark (?) in the following number sequence?

17, 9, ?, 16.5, 35, 90

• A. 5
• B. 15
• C. 10
• D. 20
• E. None of these

Answer 1

The correct option is C 10

Let's try to understand how we got 9 from 17.
$17\times 0.5+0.5=9$
Now in this equation, we are multiplying 17 with 0.5 and again we are adding 0.5 to the product. The result is 9. Let's call 0.5 be the multiplying factor.
Same logic is used to get the next numbers in the sequence with multiplying factors being increased every time by a difference of 0.5.
$9\times 1+1=10$
$10\times 1.5+1.5=16.5$
$16.5\times 2+2=35$
$35\times 2.5+2.5=90$