Moving 1 match stick in the number 9 will make the biggest number 965.
Step-by-step explanation:
Given number is 369. The number 3 is made of 5 match sticks, 6 is made of 6 match sticks and 9 is also made of 6 match sticks.
Let us try the possibilities of moving 1 match stick to make the biggest number.
(a) If the left upper match stick from 9 is moving to right upper position of 6, then the number will be 383.
(b) If the left bottom match stick from 6 is moving to left bottom position of 9, then the number will be 358.
(c) If the right upper match stick from 9 is moving to right upper position of 6, then the number will be 385.
(d) If the right upper match stick from 9 is moving to left upper position of 3, then the number will be 965.
The above four trials are shown in the below attachment.
Among these four possibilities, 965 is the biggest number.