How many two-digit decimals are greater than 5.1 and less than 5.9?
比5.1大，比5.9小的两位小数有多少个．
<gadget id="calculator">89 - 11</gadget>
<output>78</output>

<gadget id="calculator">78 + 1</gadget>
<output>79</output>

<result>79</result>