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Mathematics

Find the sum:

(i) 25+310\dfrac{2}{5} + \dfrac{3}{10}

(ii) 712+58\dfrac{7}{12} + \dfrac{5}{8}

(iii) 47+314-\dfrac{4}{7} + \dfrac{3}{14}

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Answer

(i) Given, 25+310\dfrac{2}{5} + \dfrac{3}{10}

L.C.M. of 5 and 10 = 10.

25+3102×25×2+310410+3104+310710.\Rightarrow \dfrac{2}{5} + \dfrac{3}{10} \\[1em] \Rightarrow \dfrac{2 \times 2}{5 \times 2} + \dfrac{3}{10} \\[1em] \Rightarrow \dfrac{4}{10} + \dfrac{3}{10} \\[1em] \Rightarrow \dfrac{4 + 3}{10} \\[1em] \Rightarrow \dfrac{7}{10}.

Hence, 25+310=710\dfrac{2}{5} + \dfrac{3}{10} = \dfrac{7}{10}.

(ii) Given, 712+58\dfrac{7}{12} + \dfrac{5}{8}

L.C.M. of 12 and 8 = 24.

712+587×212×2+5×38×31424+152414+15242924.\Rightarrow \dfrac{7}{12} + \dfrac{5}{8} \\[1em] \Rightarrow \dfrac{7 \times 2}{12 \times 2} + \dfrac{5 \times 3}{8 \times 3} \\[1em] \Rightarrow \dfrac{14}{24} + \dfrac{15}{24} \\[1em] \Rightarrow \dfrac{14 + 15}{24} \\[1em] \Rightarrow \dfrac{29}{24}.

Hence, 712+58=2924\dfrac{7}{12} + \dfrac{5}{8} = \dfrac{29}{24}.

(iii) Given, 47+314-\dfrac{4}{7} + \dfrac{3}{14}

L.C.M. of 7 and 14 = 14.

47+3144×27×2+314814+3148+314514.\Rightarrow -\dfrac{4}{7} + \dfrac{3}{14} \\[1em] \Rightarrow -\dfrac{4 \times 2}{7 \times 2} + \dfrac{3}{14} \\[1em] \Rightarrow -\dfrac{8}{14} + \dfrac{3}{14} \\[1em] \Rightarrow \dfrac{-8 + 3}{14} \\[1em] \Rightarrow -\dfrac{5}{14}.

Hence, 47+314=514-\dfrac{4}{7} + \dfrac{3}{14} = -\dfrac{5}{14}.

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