We have a trick for multiple 2 number close to 100

The trick is:

first, find the different between first number and 100

take 99-100 = -1
do the same with second number we get 1*

multiple 2 numbers: (-1)*(-1)= 01
so we get --01

take the first number (or second number) and add the different*of another number*

remember that we add the different of another number

99 + (-1) = 98

We get 9801

for ex:

97 * 98

--06

answer: 9506