Answer :
Multiples of 10 lie between 10 and 200 are in A.P.
20 , 30 , 40 , _ _ _ _ _ _ _ _ , 190
a = 20 , d = 10 , tn = 190
tn = a + ( n - 1 ) × d
190 = 20 + ( n - 1 ) × 10
190 = 20 + 10n - 10
190 = 20 - 10 + 10n
190 = 10 + 10n
10n = 190 - 10
10n = 180
n = 180/10
n = 18
Therefore
There are 18 multiples of 10 between 10 and 200.