let the number of N50 notes = x let the number of N20 notes = yfrom the first statement x + y = 13.....(1)from the second statement 50x + 20y = 530 ......(2)dividing through by 10, we have 5x + 2y = 53 ....(20solving simultaneously by eliminating x + y = 12....(1)5x + 2y = 53.....(2)multiply eqn (1) by 2multiply eqn (2) by 1 2x + 2y = 26-5x + 2y = 53 -3x = -27 x = 9substitute x = 9 into equation (1)x + y = 13y = 13 - x= 13 - 9 = 4y = 4the number of N50 notes = 9