a) $\sqrt{0.25}-\sqrt{0.49}=\sqrt{(0.5)^{2}}-\sqrt{(0.7)^{2}}=0.5-0.7=-0.2$;
b) $0.2\times \sqrt{100}-\sqrt{0.25}=0.2\times 10-0.5=2-0.5=1.5$
a) $\sqrt{0.25}-\sqrt{0.49}=\sqrt{(0.5)^{2}}-\sqrt{(0.7)^{2}}=0.5-0.7=-0.2$;
b) $0.2\times \sqrt{100}-\sqrt{0.25}=0.2\times 10-0.5=2-0.5=1.5$