q.18 (pattern question) 125, on every odd power the number ends in 125 and on every even power the number ends in 625. 15 is odd, so the answer is 125
q.19 20, find the HCF (highest common factor of both) which is 4, then divide into both numbers, 20/4 = 5 and 16/4=4. 5x4=20.
q.48 D (i think...