Answer:
The sum of the odd numbers between 11 and 199 inclusive
= 9,975
Step-by-step explanation:
Old numbers between 11 and 199 are:
11 13 15 17 19 21 23 25 27 29 = 200
31 33 35 37 39 41 43 45 47 49 = 400
51 53 55 57 59 61 63 65 67 69 = 600
71 73 75 77 79 81 83 85 87 89 = 800
91 93 95 97 99 101 103 105 107 109 = 1,000
111 113 115 117 119 121 123 125 127 129 = 1,200
131 133 135 137 139 141 143 145 147 149 = 1,400
151 153 155 157 159 161 163 165 167 169 = 1,600
171 173 175 177 179 181 183 185 187 189 = 1,800
191 193 195 197 199 = 975
Total sum = 9,975
Classify the odd numbers into 10 columns, then add each row. Start by adding the first row, which equals 200. Each successive row of the old numbers will equal 200 more than the previous row sum. At the end, add all the row sums to get the sum of the old numbers from 11 to 199.
