Dear Subrat ji,
First of all, let me congratulate you as the first person on the forum who have come out and asked a query in a new thread.
I’m suggesting the solutions not by giving out the answer, but by giving out the example which can be referred to so that you can try it out once again on your own. Still if you find any difficulty, please feel free to reply to the post.
a) 901 WITH 990 – can be done as 901 x 99 and after the operation, a zero (the last digit of 990) can be added back to the answer. To perform 901 x 99, refer to e.g.(v) in Lesson 9
b) 9090 WITH 9990 – same like above….remove the last zeros in 9990 and 9090 and perform the operation as 909 x 999. Later add back the two zeros that you removed.
c) 990 WITH 9172,
d) 9911 WITH 990,
e) 9990 WITH 2746,
f) 90 WITH 86,
g) 813 WITH 9900,
h) 900 WITH 8710.
All the above examples can done like e.g. a) and b), i.e. by removing the zeros in the end.
Hope this has helped.
With Prem & Om,