Question

How many two-digit numbers have digits whose difference is 3?

Answer 1

Heya

We have to find number of :
$(ab)_{10}$
such that ( a - b ) = +3

∆ Maximum a = 9 => maximum b = 6
∆ Minimum b = 0 => minimum a = 3

Now, such numbers are :

$(30,41,52,63,74,85,96)$
for which, a>b

Similarly, for b>a, we have the numbers :
$(14,25,...,69)$

which are inverse of the above numbers

Counting these, we have 13 such numbers in total that follow the above situation.