multiplication really simple

Question

whats 56 x 77 i cant seem to be able to put thin in my calculator

Answer 1

4312

56x77 = 4312

56x7 = 392

56x70 = 3920

3920 +

392 =

4312

one way to check the answer is add the digits up, reducing them to one digit

5+6 = 11, 1+1= 2

7+7 = 14, 1+4= 5

2x5 = 10, 1+0=1

the answer should have the same digit 1 as its sum of digits

4312 is 4+3+1+2 = 10, 1+0=1

this is called the "rule of 9's" same as dividing by 9 and keeping the remainder

56/9 = 6 with remainder of 2

77/9 = 8 with remainder of 5

2x5 = 10, 10/9 = 1 with remainder of 1

the answer should similarly reduce to a remainder of 1 when divided by 9

4312/9 = 479 with remainder of 1

1 remainder from the product =1 remainder in the answer, that means at least about 90% that you got it right