The average weight of R, P and K is 40 kg. If the average weight of P and K is 45 kg and average weight of R and K is 35 kg, then what is the weight of K?

40 kg

Let's assume weight of R, P & K are also denoted by same letters

R + P + K = 40 x 3 =120      -------------- 1

P + K = 45 x 2 = 90             ---------------2

R + K = 35 x 2 = 70             ---------------3

Add. equation 2 & 3

R + P + 2K = 160                  ---------------4

From 1 and 4

(160 - 2K) + K = 120

K = 40