The pH of 40 ml of a 0.02 M HCl will not be changed by adding

 Initial pH of 40 ml of a 0.02 M HCl: pH = $-log\left[H^{+}\right]$ = -log[0.02] = 1.70

pH of solution after adding 36 ml of same concentrated HCl solution = -log[0.02] = 1.70

Since the pH doesn’t change but only the volume which is changed.