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When a letter of less value is written before one of greater value, their difference is expressed:

$\mathrm {IV=4,\qquad XL=40,\qquad XC=90}$

When a bar is placed over a letter, its value is multipled by 1000:

$\mathrm {{\overline {V}}=5000,\qquad {\overline {XIV}}=14,000}$

$\mathrm {I} \$	$\mathrm {1} \$	$\mathrm {XI} \$	$\mathrm {11} \$	$\mathrm {XXI} \$	$\mathrm {21} \$	$\mathrm {D} \$	$\mathrm {500} \$
$\mathrm {II} \$	$\mathrm {2} \$	$\mathrm {XII} \$	$\mathrm {12} \$	$\mathrm {XXX} \$	$\mathrm {30} \$	$\mathrm {DC} \$	$\mathrm {600} \$
$\mathrm {III} \$	$\mathrm {3} \$	$\mathrm {XIII} \$	$\mathrm {13} \$	$\mathrm {XL} \$	$\mathrm {40} \$	$\mathrm {DCC} \$	$\mathrm {700} \$
$\mathrm {IV} \$	$\mathrm {4} \$	$\mathrm {XIV} \$	$\mathrm {14} \$	$\mathrm {L} \$	$\mathrm {50} \$	$\mathrm {DCCC} \$	$\mathrm {800} \$
$\mathrm {V} \$	$\mathrm {5} \$	$\mathrm {XV} \$	$\mathrm {15} \$	$\mathrm {LX} \$	$\mathrm {60} \$	$\mathrm {CM} \$	$\mathrm {900} \$
$\mathrm {VI} \$	$\mathrm {6} \$	$\mathrm {XVI} \$	$\mathrm {16} \$	$\mathrm {LXX} \$	$\mathrm {70} \$	$\mathrm {M} \$	$\mathrm {1000} \$
$\mathrm {VII} \$	$\mathrm {7} \$	$\mathrm {XVII} \$	$\mathrm {17} \$	$\mathrm {LXXX} \$	$\mathrm {80} \$	$\mathrm {MM} \$	$\mathrm {2000} \$
$\mathrm {VIII} \$	$\mathrm {8} \$	$\mathrm {XVIII} \$	$\mathrm {18} \$	$\mathrm {XC} \$	$\mathrm {90} \$	$\mathrm {\overline {IV}} \$	$\mathrm {4000} \$
$\mathrm {IX} \$	$\mathrm {9} \$	$\mathrm {XIX} \$	$\mathrm {19} \$	$\mathrm {C} \$	$\mathrm {100} \$	$\mathrm {\overline {V}} \$	$\mathrm {5000} \$
$\mathrm {X} \$	$\mathrm {10} \$	$\mathrm {XX} \$	$\mathrm {20} \$	$\mathrm {CC} \$	$\mathrm {200} \$	$\mathrm {\overline {IX}} \$	$\mathrm {9000} \$

Write in figures the following:

$\mathrm {XXIX} \$	$\mathrm {CIX} \$	$\mathrm {LXIV} \$	$\mathrm {MCMXI} \$
$\mathrm {XLV} \$	$\mathrm {CCXIX} \$	$\mathrm {LXXV} \$	$\mathrm {MCIV} \$
$\mathrm {LXXVI} \$	$\mathrm {MXCV} \$	$\mathrm {MDCV} \$	$\mathrm {{\overline {X}}DLII} \$
$\mathrm {DXC} \$	$\mathrm {XXXIX} \$	$\mathrm {MCII} \$	$\mathrm {{\overline {CD}}CC} \$
$\mathrm {XCIV} \$	$\mathrm {DCXC} \$	$\mathrm {DCCX} \$	$\mathrm {DLIV} \$

ADDITION.

Addition is the process of finding the sum of two or more numbers of the same kind.

The sign of addition is $+\$, and is read plus.

The child should be taught the numbers through 10, and drilled until he responds automatically to any combination.

Primary ideas of numbers and of operations should be gained from objects, but gradually the objects should be eliminated as the pupil progresses in his knowledge of number.

The following combinations should be thoroughly mastered as a foundation for effective work in arithmetic:

$2+0=2\$	$4+0=4\$	$5+0=5\$	$6+0=6\$
$1+1=2\$	$3+1=4\$	$4+1=5\$	$5+1=6\$
$\$	$2+2=4\$	$3+2=5\$	$4+2=6\$
$\$	$1+3=4\$	$2+3=5\$	$3+3=6\$
$3+0=3\$	$\$	$1+4=5\$	$2+4=6\$
$2+1=3\$	$\$	$\$	$1+5=6\$
$1+2=3\$
$\$