Question

Kevin is 3 times as old as Daniel. 4 years ago, Kevin was 5 times as old as Daniel. How old is kevin now?

Answer 1

K=kevin age
d=daniel ae

k is 3 times d
k=3d

4 years ago (k-4 and d-4)
kevin was 5 times as old as dan

k-4=5(d-4)

we have
k=3d
and
k-4=5(d-4)
sub 3d for k in second euaiton
3d-4=5(d-4)
3d-4=5d-20
minus 3d both sides
-4=2d-20
add 20 both sides
16=2d
divide 2
8=d
sub back
k=3d
k=3(8)
k=24

kevin is 24

Answer 2

K = Kevin's age
D = Daniel's age

K = 3D

K - 4 = 5(D - 4)

Plug in 3D for the K values in the second equation.

3D - 4 = 5(D - 4)   Use the Distributive Property
3D - 4 = 5D - 20   Add 4 to both sides
     3D = 5D - 16     Subtract 5D from both sides
    -2D = -16            Divide both sides by -2
       D = 8 
 Now, plug that D value into the original equation.

K = 3D    Plug in the D value
K = 3(8)   Multiply
K = 24

Finally, you can double check your math.

4 years ago, Daniel would've been 4 and Kevin would be 20, so Kevin would've been 5 times as old as Daniel.  And 8 x 3 = 24.

So, Kevin is 24.