31.
3897 x 999 = 3897 x (1000 -1)
= 3897 x 1000 – 3897 x 1
= 3897000 – 3897 = 3893103
3897000
-2519
3893103
32.
7259 x 9999 = 72519 x (10000 – 1)
= 72519 x 10000 – 72519
x 1
= 725190000 – 72519 =
72117481 725190000
-72519 
725117481
33.
2056 x 987 = 2056 x (1000 – 13)
=2056 x 1000 – 2056 x
13 2056000
=2056000 – 2672 =
2029272 - 26728
2029272
34.
1904 x 1904 = (1904)² =(1900 + 4)²
= (1900)² +
4²
+ x 21900 x 4 = 3610000 + 16 +15200
= 3610016 + 15200 =
3625216.
35.
1397 x 1397 = (1397)² = (1400 – 3)²
