If David will give seven cookies to each five friends, first multiply the two numbers. So, 7 x 5 = 35. Now you know the number of cookies that David will give, you should now subtract it. So, 48 - 35 = 13. 13 cookies are left to David.
So the mathematical sentence here is: 48 -(7 x 5). To do this question, use the order of operations.
Hope this helps. :)