Sipser 2.28 c. {w | the number of a's is at least the number of b's}

2.28 c. {w | the number of a's is at least the number of b's}

Solution:

S → aSbS | bSaS | aS | ε

aSbS | bSaS generates equal number of a and b. Then aS will help you to generate as many a you want. But it is ambiguous.