diff --git a/manuscript/09_ht.md b/manuscript/09_ht.md
index 2aefb60..7bb33ff 100644
--- a/manuscript/09_ht.md
+++ b/manuscript/09_ht.md
@@ -291,7 +291,7 @@ Consider now testing {$$}H_0 : \mu_1 = \mu_2{/$$}. Our statistic is
 \frac{\bar X_1 - \bar X_2 - (\mu_1 - \mu_0)}{S_p\sqrt{\frac{1}{n1} + \frac{1}{n_2}}}.
 {/$$}
 
-For the equal variance case and and
+For the equal variance case and
 
 {$$}
 \frac{\bar X_1 - \bar X_2 - (\mu_1 - \mu_0)}{\sqrt{\frac{S_1^2}{n1} + \frac{S_2^2}{n_2}}}.