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(a) Private saving = Y-T-C

Private saving = 5000-1000-250-0.75(5000-1000)

Private saving = 750

Public saving = T - G

Public saving = 1000-1000

Public saving = 0

National saving = S = private saving+ public saving

National saving = 750

(B)  Equilibrium interest rate = S + I

750 = 1000 - 50r

-50r = 750 - 1000

-50r = -250

50r = 250

r = 250/50

r = 5%

(c) Private saving is unchanged

Public saving = 1000 - 1250

Public saving = - 250

(d) The new equilibrium interest rate

750 (-250) = 1000-50r

500 = 1000 - 50r

- 50r = 500 - 1000

- 50r = -500

-50r = 500

r = 500/50

r = 10%