When Xiao Ma calculated the average of 18 numbers, he mistakenly believed that there was a decimal point between the ones and tens digits of one of the integers, and the obtained average was 7.8 smaller than the correct result. So, what is the wrong number?
小马在计算18个数的平均数时，误认为其中一个整数的个位和十位之间有小数点，得到的平均数比正确结果小7.8，那么，这个被看错的数原来是多少．
<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / 180</gadget>
<output>1/180 = around 0.005556</output>

<gadget id="calculator">(1/18) - (1/180)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">7.8 / (1/20)</gadget>
<output>156</output>

<result>156</result>