To find the probability that the mom is at the front of the line:

Therefore the answer is 1/5.
Hope it helps!
I think the answer is 1 but I can’t see the picture
Step-by-step explanation:
The required sum
=(1+2+3+...+199)−(3+6+9+...+198)−(5+10+15+...+195)+(15+30+45+...+195)
=2199(1+199)−266(3+198)−239(5+195)+213(15+195)
=199×100−33×201−39×100+13×105=10732