fixed a few typos (#912)

Author: 708-145

tutorials/optimization/1_quadratic_program.ipynb

@@ -218,7 +218,7 @@
    "metadata": {},
    "source": [
     "The `QuadraticProgram` supports three types of variables:\n",
-    "- Binary varible\n",
+    "- Binary variable\n",
     "- Integer variable\n",
     "- Continuous variable\n",
     "\n",
@@ -607,10 +607,10 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "You can substitue some of variables with constants or other variables.\n",
+    "You can substitute some of variables with constants or other variables.\n",
     "More precicely, `QuadraticProgram` has a method `substitute_variables(constants=..., variables=...)` to deal with the following two cases.\n",
     "- $x \\leftarrow c$: when `constants` have a dictionary `{x: c}`. \n",
-    "- $x \\leftarrow c y$: when `variables` have a dictuinary `{x: (y, c)}`."
+    "- $x \\leftarrow c y$: when `variables` have a dictionary `{x: (y, c)}`."
    ]
   },
   {
@@ -691,7 +691,7 @@
    "metadata": {},
    "source": [
     "You cannot substitute variables multiple times. \n",
-    "The metdod raises an error in such a case."
+    "The method raises an error in such a case."
    ]
   },
   {
@@ -776,7 +776,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.4"
+   "version": "3.7.7"
   }
  },
  "nbformat": 4,