23. 4 1/2+(-3/4)=

23. $$4 \frac{1}{2}+(-\frac{3}{4}) = 4 \frac{1}{2} - \frac{3}{4} = 4 \frac{2-3}{4} = 3 \frac{6-3}{4} = 3 \frac{3}{4}$$

Ответ: $$3 \frac{3}{4}$$