Instead of the expected frequencies, you can put proportional values; eg. instead of 5,5,10 you can put 1,1,2.
In the following table, d.f. is the number of degrees of freedom. 5,
,95 are the 5th,
95th percentiles
examples
d.f. 5 10 25 50 75 90 95
1 0.00393 0.0158 0.102 0.455 1.32 2.71 3.84
2 0.103 0.211 0.575 1.39 2.77 4.61 5.99
3 0.352 0.584 1.21 2.37 4.11 6.25 7.81
4 0.711 1.06 1.92 3.36 5.39 7.78 9.49
5 1.15 1.61 2.67 4.35 6.63 9.24 11.1
6 1.64 2.20 3.45 5.35 7.84 10.6 12.6
7 2.17 2.83 4.25 6.35 9.04 12.0 14.1
8 2.73 3.49 5.07 7.34 10.2 13.4 15.5
9 3.33 4.17 5.90 8.34 11.4 14.7 16.9
10 3.94 4.87 6.74 9.34 12.5 16.0 18.3
11 4.57 5.58 7.58 10.3 13.7 17.3 19.7
12 5.23 6.30 8.44 11.3 14.8 18.5 21.0
13 5.89 7.04 9.30 12.3 16.0 19.8 22.4
14 6.57 7.79 10.2 13.3 17.1 21.1 23.7
15 7.26 8.55 11.0 14.3 18.2 22.3 25.0
16 7.96 9.31 11.9 15.3 19.4 23.5 26.3
17 8.67 10.1 12.8 16.3 20.5 24.8 27.6
18 9.39 10.9 13.7 17.3 21.6 26.0 28.9
19 10.1 11.7 14.6 18.3 22.7 27.2 30.1
20 10.9 12.4 15.5 19.3 23.8 28.4 31.4
25 14.6 16.5 19.9 24.3 29.3 34.4 37.7
30 18.5 20.6 24.5 29.3 34.8 40.3 43.8
35 22.5 24.8 29.1 34.3 40.2 46.1 49.8
40 26.5 29.1 33.7 39.3 45.6 51.8 55.8
45 30.6 33.4 38.3 44.3 51.0 57.5 61.7
50 34.8 37.7 42.9 49.3 56.3 63.2 67.5
55 39.0 42.1 47.6 54.3 61.7 68.8 73.3
65 47.4 50.9 57.0 64.3 72.3 80.0 84.8
75 56.1 59.8 66.4 74.3 82.9 91.1 96.2
85 64.7 68.8 75.9 84.3 93.4 102 108
100 77.9 82.4 90.1 99.3 109 118 124
How to roughly determine the value in a case not present in the table: 6 degrees of freedom, 40%
6 d.f, 25% → 3.45, 50% → 5.35
(x - 5.35) / (3.45 - 5.35) = (50 - 40) / (50 - 25)
x = (50 - 40) / (50 - 25) * (3.45 - 5.35) + 5.35 = 4.59