Q1 .5 * 9

STEP 1 :

First of all subtract 5 to 9
= 5 - 1
= 4
= first part of answer will be 4 /

STEP 2 :

Now subtract 4 to 9
= 9 - 4
= 5
= second part of answer will be 4 / 5

so answer is 45

Q2 .12 * 99

STEP 1 :

First of all subtract 12 to 99
= 12 - 1
= 11
= first part of answer will be 11 /

STEP 2 :

Now subtract 11 to 99
= 99 - 11
= 88
= second part of answer will be 11 / 88

so answer is 1188

Q3 .981 * 999

STEP 1 :

First of all subtract 981 to 999
= 981 - 1
= 980
= first part of answer will be 980 /

STEP 2 :

Now subtract 980 to 999
= 999 - 980
= 19
= second part of answer will be 980 / 19

so answer is 98019

Note : If we have to multiply numbers like 4 * 99 so we will make 4 as two digit number like 04 * 99.