If 20 % of the income is save then MPS =0.2.
Multiplier(k) => Change in income / change in investment = 1/ MPS
=> change in income/ 10,000 = 1/0.2
=> change in income/ 10,000 = 5
=> change in income = 5 * 10,000 = 50,000
Hence, national income is increased by 50,000.