Question

Consider the numbers 7, 7 x 7,7 x 7 x 7,7.x 7 x 7 x 7,7 × 7×7×7×7.

Find the right-most digit of each of these numbers. What do you observe? Based on your observation, find the right-most digit of the number 7 × 7 × 7 × 7......... 11 times.( ans 3 ) .
EXPLAIN IT. ​

Answer 1

Answer:

Number of selections of 7 digits out of the digit 1,2,3,.....,9=

9

C

7

Number of digits out of these 7 selected digits excluding the greatest digit =6

These 6 digits can be divided in two group each having 3 digits

6!

=

6

C

3

×

2!

1

But the 3 digits on one side can go on the other side.

∴Required number of ways

=

9

C

7

.

6

C

3

×

2!

2

=

9

C

2

.

6

C

3