What will be the value of multiplier if 40% of the additional income is saved?

2.5

The formulae for Keynesian Investment Multiplier is:

k = \(\frac{1 }{\text 1 - MPC }\)

If 40% of increase in income is saved then MPS is 0.4 and the value of MPC can be written as 0.6 as, MPC = 1 - MPS

So, 

k = \(\frac{1 }{\text 1 - MPC }\)

k = \(\frac{1 }{\text 1 -  0.6 }\)

k = \(\frac{1 }{\text 0.4 }\)

k = \(\frac{10 }{\text 4}\)

k = 2.5