ANSWER

EXPLANATION
It was given that, 10 people can paint a building in 5days.
We can write the ratio,

Now we want to find how much of the building
7 people could paint in the same 5 days working at the same rate.
Let it be in the ratio,

Then we can write and solve the following proportional equation for x,

We can rewrite this as a fraction to get,

Let us now cross multiply to get,

We divide both sides by 10 to obtain,

This means the 7 people can only paint a fraction ( 70%) of the building and not the whole building.