For Question number 1

by Daya Singh Sandhu
(Amritsar)

Actually the answer by hit and trial for 3x0 to be divisible 8 ... value of x=2 also holds true as 320 is divisible by 8 but the 65320 is not divisible by 80. so basically the method under taken is wrong..it should be that 53x0 should be divisible by 16. for which the answer will come out as x =6 only.

Fault can be seen in your method like this.

if you have said that, as the number should be divisible by 2 and 5 last digit should be 0. which is true. Later on you have probably dropped 0 from 80 reducing it to 8. but at the same time you faulted by not removing 0 from 653x0 to 653x for the check on divisibility by 8. which probably would have given you the test of last digits (53x) to be divisible by 8 giving you the correct answer x=6. or you should have gone for the divisibility by 16 checking for the last 4 digits( as solved by me above).