Question

Using the di ts 1,2,3,4 only once to form 4 digit number , how
many of them are divisible by 11?

Answer 1

Step-by-step explanation:

For number to be divisible by 11 sum of alternate digits must be equal.

If 1 is in thousands place possible numbers 1243 , 1342

If 1 is in hundreds place possible numbers 2134 , 3124

If 1 is in tens place possible numbers 4312 , 4213

If 1 is in units place possible numbers 3421 , 2431

8 without repetition

Repetition is allowed

aaaa-1111,2222,3333,4444 ……… 4 Cases

aabb- 1122,2244………………. 4x3 = 12 cases

abba-1221,2332,4114,………. 4x3 = 12 Cases

abac- 2123, 3212, 2321, 1232 4 Cases

32 more with repetition

So total = 8+32=40