If `.^(n)P_(r) = 720` and `.^(n)C_(r) = 120`, then find r.
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If .^(n)P_(r)=720 and .^(n)C_(r)=120 then find the value of r.

If ""^(n)P_(r) = 840 and ""^(n)C_(r) = 35 , then r is equal to ………… .

If ""^(n)C_(r -1) = 36, ""^(n)C_(r) = 84 " and " ""^(n)C_(r +1) = 126 , then find the value of ""^(r)C_(2) .

If ""^n C_(r-1) = 36, ""^(n) C_(r) = 84 and ""^(n) C_(r+1) = 126 then find the value of r.

If .^(n)C_(r-1)=36, .^(n)C_(r)=84 and .^(n)C_(r+1)=126 , find n and r.

If ^n C_r=84 , and ^n C_(r-1)=36 , and r = 1 , then find the value of ndot

If ^nC_r=84 ,^n C_(r-1)=36 ,a n d^n C_(r+1)=126 , then find the value of ndot

.^(n)C_(r)+2.^(n)C_(r-1)+.^(n)C_(r-2)=

If .^(n)C_(r-1): .^(n)C_(r): .^(n)C_(r+1)=3:4:5 , find the values of n and r.

If sum _(r =1) ^(n ) T _(r) = (n +1) ( n +2) ( n +3) then find sum _( r =1) ^(n) (1)/(T _(r))