Challenge Question 8: 21 * ? ? = ? ? 12
Going by the Last by the last digit, we know that that the value of second ? would be 2. So it becomes
2 1
a 2 *
—-
b c 1 2
—-
Going by ‘Vertically and cross wise’ we know that 2*2 + a*1 = c 1
i.e. 4 + a = c 1 –> number that gives 1 in units place of the answer when 4 gets added to it is 7
which makes the above 4 + 7 = 1 1 means a = 7 and there is a carry on of 1 that needs to be added to the hundred’s place value so
2 1
7 2 *
—-
b c(+1) 1 2
—–
7*2 is 14 and there is a carry on of 1 making it 15. So b is 1 and c is 5.
2 1 * 7 2 = 1 5 1 2
