For a $t-$curve with $\mathrm{df}=21$, find each $f-$value, and illustrate your results graphically.

a. The $t-$value having an area $0.10$to its right

b. $t_0$ a$1$

c. The $t-$value has an area $0.025$to its left (Hint: A $t-$curve is symmetric at about 0.)

d. The two $t-$values that divide the area under the curve into a middle $0.90$area and two outside areas of $0.05$

For a $t-$curve with $\mathrm{df}=21$

Degrees of freedom of the $t-$curve is $21$

We need to acquire the $t-$ value with the area $0.10$ to its right, i.e. $t_{0.10}$, from table-IV of APPENDIX-A.

For $df=21,t_{0.10}=1.323$

Create the Graph plot

From table-IV of APPENDIX - A, we get For $df=21,t_{0.01}=2.518$

Create the Graph plot

We need to get $t-$the value with the area $0.025$ to its left.

Curve is symmetric around $t$ As a result, the negative of the $t-$ value with area $0.025$ to its left is identical to the $t-$ value with area $0.025$ to its right.

i.e. With $t-$value having area $0.025$to its left $=-t_{0.025}$

$=-2.080$

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The two $t-$values that split the area under the curve into a middle $0.90$area and outer $0.05$areas must be obtained. i.e. We have to obtain $-t_{0.05}$and $t_{0.05}$for $df=21$

Because $t-$curve is symmetric about $0$

$\therefore$From table-IV,

For $df=21,t_{0.05}=1.721$

$\therefore$The required two $t-$values are $-1.721$and $1.721$

Create the Graph plot