Question

How many integers between 10 and 20 are multiples of 3 but not 2?

10 and 20 inclusive
Please do it algebraically.

Answer 1

Explanation:

y=3x,x≠2t,t∈ N,10≤y≤20

if y=10,3x=10,

x=10/3=31/3.

so x=4

but x≠4

so first x=5

number is 3×5=15

again we consider 20=3x

x=20/3=6 2/3

x=6

but x is not even or multiple of 2

so x=5

y=3×5=15

so only required number is 15.