My basketball team has eight games next month. We're pretty good; we have a 2/3 chance to win in each game. What is the probability we have a winning streak of at least four games at some point during the month?
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | FOUR IN A ROW |
W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{32}}}{{\mathtt{243}}}} = {\mathtt{0.131\: \!687\: \!242\: \!798\: \!353\: \!9}}$$ | |||
L | W | W | W | W | ||||
L | W | W | W | W | L | $${\mathtt{3}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{16}}}{{\mathtt{243}}}} = {\mathtt{0.065\: \!843\: \!621\: \!399\: \!177}}$$ | ||
L | W | W | W | W | L | |||
L | W | W | W | W | L |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | FIVE IN A ROW |
W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{64}}}{{\mathtt{729}}}} = {\mathtt{0.087\: \!791\: \!495\: \!198\: \!902\: \!6}}$$ | ||
L | W | W | W | W | W | |||
L | W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}} = {\mathtt{0.029\: \!263\: \!831\: \!732\: \!967\: \!5}}$$ | |
L | W | W | W | W | W | L |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | SIX IN A ROW |
W | W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}} = {\mathtt{0.058\: \!527\: \!663\: \!465\: \!935\: \!1}}$$ | |
L | W | W | W | W | W | W | ||
L | W | W | W | W | W | W | L | $${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}} = {\mathtt{0.009\: \!754\: \!610\: \!577\: \!655\: \!8}}$$ |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | SEVEN IN A ROW |
W | W | W | W | W | W | W | L | |
L | W | W | W | W | W | W | W |
I TRIED TO PUT ALL THIS INTO A TABLE BUT THE TABLE DID NOT COPE VERY WELL
FOUR IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{32}}}{{\mathtt{243}}}} = {\mathtt{0.131\: \!687\: \!242\: \!798\: \!353\: \!9}}$$
$${\mathtt{3}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{16}}}{{\mathtt{243}}}} = {\mathtt{0.065\: \!843\: \!621\: \!399\: \!177}}$$
FIVE IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{64}}}{{\mathtt{729}}}} = {\mathtt{0.087\: \!791\: \!495\: \!198\: \!902\: \!6}}$$
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}} = {\mathtt{0.029\: \!263\: \!831\: \!732\: \!967\: \!5}}$$
SIX IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}} = {\mathtt{0.058\: \!527\: \!663\: \!465\: \!935\: \!1}}$$
$${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}} = {\mathtt{0.009\: \!754\: \!610\: \!577\: \!655\: \!8}}$$
SEVEN IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{7}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\mathtt{0.039\: \!018\: \!442\: \!310\: \!623\: \!4}}$$
EIGHT IN A ROW
$${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{8}}} = {\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\mathtt{0.039\: \!018\: \!442\: \!310\: \!623\: \!4}}$$
$${\frac{{\mathtt{32}}}{{\mathtt{243}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{16}}}{{\mathtt{243}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{729}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\frac{{\mathtt{112}}}{{\mathtt{243}}}} = {\mathtt{0.460\: \!905\: \!349\: \!794\: \!238\: \!7}}$$
Probabilty of a winning streak of 4 = (2/3)^4 = 16/81
Probabilty of a winning streak of 5 = (2/3)^5 = 32/243
Probabilty of a winning streak of 6 = (2/3)^6 = 64/729
Probabilty of a winning streak of 7 = (2/3)^7 = 128/2187
Probabilty of a winning streak of 8 = (2/3)^8 = 256/6561
So the total probability of winning four or more in a row is
16 / 81 + 32 / 243 + 64 / 729 + 128 / 2187 + 256 / 6561 = 3376 / 6561 = about 51.46%
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | FOUR IN A ROW |
W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{32}}}{{\mathtt{243}}}} = {\mathtt{0.131\: \!687\: \!242\: \!798\: \!353\: \!9}}$$ | |||
L | W | W | W | W | ||||
L | W | W | W | W | L | $${\mathtt{3}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{16}}}{{\mathtt{243}}}} = {\mathtt{0.065\: \!843\: \!621\: \!399\: \!177}}$$ | ||
L | W | W | W | W | L | |||
L | W | W | W | W | L |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | FIVE IN A ROW |
W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{64}}}{{\mathtt{729}}}} = {\mathtt{0.087\: \!791\: \!495\: \!198\: \!902\: \!6}}$$ | ||
L | W | W | W | W | W | |||
L | W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}} = {\mathtt{0.029\: \!263\: \!831\: \!732\: \!967\: \!5}}$$ | |
L | W | W | W | W | W | L |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | SIX IN A ROW |
W | W | W | W | W | W | L | $${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}} = {\mathtt{0.058\: \!527\: \!663\: \!465\: \!935\: \!1}}$$ | |
L | W | W | W | W | W | W | ||
L | W | W | W | W | W | W | L | $${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}} = {\mathtt{0.009\: \!754\: \!610\: \!577\: \!655\: \!8}}$$ |
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | SEVEN IN A ROW |
W | W | W | W | W | W | W | L | |
L | W | W | W | W | W | W | W |
I TRIED TO PUT ALL THIS INTO A TABLE BUT THE TABLE DID NOT COPE VERY WELL
FOUR IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{32}}}{{\mathtt{243}}}} = {\mathtt{0.131\: \!687\: \!242\: \!798\: \!353\: \!9}}$$
$${\mathtt{3}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{4}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{16}}}{{\mathtt{243}}}} = {\mathtt{0.065\: \!843\: \!621\: \!399\: \!177}}$$
FIVE IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{64}}}{{\mathtt{729}}}} = {\mathtt{0.087\: \!791\: \!495\: \!198\: \!902\: \!6}}$$
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{5}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}} = {\mathtt{0.029\: \!263\: \!831\: \!732\: \!967\: \!5}}$$
SIX IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}} = {\mathtt{0.058\: \!527\: \!663\: \!465\: \!935\: \!1}}$$
$${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{6}}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right)}^{{\mathtt{2}}} = {\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}} = {\mathtt{0.009\: \!754\: \!610\: \!577\: \!655\: \!8}}$$
SEVEN IN A ROW
$${\mathtt{2}}{\mathtt{\,\times\,}}{\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{7}}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{3}}}}\right) = {\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\mathtt{0.039\: \!018\: \!442\: \!310\: \!623\: \!4}}$$
EIGHT IN A ROW
$${\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}^{{\mathtt{8}}} = {\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\mathtt{0.039\: \!018\: \!442\: \!310\: \!623\: \!4}}$$
$${\frac{{\mathtt{32}}}{{\mathtt{243}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{16}}}{{\mathtt{243}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{729}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{2\,187}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{128}}}{{\mathtt{2\,187}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{64}}}{{\mathtt{6\,561}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{256}}}{{\mathtt{6\,561}}}} = {\frac{{\mathtt{112}}}{{\mathtt{243}}}} = {\mathtt{0.460\: \!905\: \!349\: \!794\: \!238\: \!7}}$$