Question: what is the product of 5 and 12

title: Mental calculation
text: If only one digit in b is larger than its corresponding digit in a , diminish the offending digit in b until it is equal to its corresponding digit in a . Then subtract further the amount b was diminished by from a . For example , to calculate 872 − 92 , turn the problem into 872 − 72 = 800 . Then subtract 20 from 800 : 780 . If more than one digit in b is larger than its corresponding digit in a , it may be easier to find how much must be added to b to get a . For example , to calculate 8192 − 732 , we can add 8 to 732 ( resulting in 740 ) , then add 60 ( to get 800 ) , then 200 ( for 1000 ) . Next , add 192 to arrive at 1192 , and , finally , add 7000 to get 8192 . Our final answer is 7460 . Another technique we can use is rounding off one of the digits ( Either the larger digit or the smaller digit to the nearest number preferably containing a single non-zero digit ) . For example , to calculate 8192 - 732 we can round off 732 to 1000 by adding 268 ( We can find the value 268 by quickly subtracting 732 from 1000 mentally . Our brain finds it easier in dealing with rounded figures . ) to it . Then we can subtract 1000 from 8192 and obtain 7192 as the answer . Now we can add 268 to 7192 to obtain 7460 as the answer . Alternatively we can exchange numbers to round off figures as in the given problem . For example , For calculating 8192 - 732 we can simply add 268 to both sides resulting in 8460 - 1000 , which is easier to calculate , resulting in 7460 . One needs to be prudent in selecting which number to be rounded off . For calculating 8192 - 732 we can round off 8192 to 9000 by adding 808 . Then we calculate 9000 - 732 resulting in 8268 . Then we can subtract 808 from 8268 to get 7460 as our answer . But as we can observe , we made the calculations difficult and lengthy . We may also perform the calculation in the traditional way but in a smart manner . For calculating 8192 - 732 we can eliminate the 2 in units place i.e. replace them with 0 . Then we can subtract 3 from 9 yielding in 6 . Finally we can subtract 7 from 81 yielding in 74 . Then we just need to rearrange the pieces to get 7460 as the answer It might be easier to start from the left ( the big numbers ) first .