(i) The like decimal numbers are 3.500, 2.430 and 0.075
First, adding the positive numbers 3.500 and 0.075
$$\begin{array}{r} & 3.500 \\ + & 0.075 \\ \hline & 3.575 \end{array}$$
Now, subtracting 2.430 from 3.575
$$\begin{array}{r} & 3.575 \\ - & 2.430 \\ \hline & 1.145 \end{array}$$
Hence, 3.5 - 2.43 + 0.075 = 1.145
(ii) The like decimal numbers are 7.840, 0.300 and 4.016
First, adding the positive numbers 7.840 and 0.300
$$\begin{array}{r} & 7.840 \\ + & 0.300 \\ \hline & 8.140 \end{array}$$
Now, subtracting 4.016 from 8.140
$$\begin{array}{r} & 8.140 \\ - & 4.016 \\ \hline & 4.124 \end{array}$$
Hence, 7.84 + 0.3 - 4.016 = 4.124
(iii) The like decimal numbers are 2.987, 1.250 and 0.540
First, adding the numbers to be subtracted 1.250 and 0.540
$$\begin{array}{r} & 1.250 \\ + &0.540 \\ \hline & 1.790 \end{array}$$
Now, subtracting 1.790 from 2.987
$$\begin{array}{r} & 2.987 \\ - & 1.790 \\ \hline & 1.197 \end{array}$$
Hence, 2.987 - 1.25 - 0.54 = 1.197
(iv) The like decimal numbers are 52.900, 231.666 and 204.000
First, adding the positive numbers 52.900 and 204.000
$$\begin{array}{rr} & 52.900 \\ + &204.000 \\ \hline & 256.900 \end{array}$$
Now, subtracting 231.666 from 256.900
$$\begin{array}{r} & 256.900 \\ - & 231.666 \\ \hline & 25.234 \end{array}$$
Hence, 52.9 - 231.666 + 204 = 25.234
(v) The like decimal numbers are 8.5700, 6.4432, 1.7000 and 0.6830
First, adding the positive numbers 8.5700 and 0.6830
$$\begin{array}{r} & 8.5700 \\ + & 0.6830 \\ \hline & 9.2530 \end{array}$$
Adding the numbers to be subtracted 6.4432 and 1.7000
$$\begin{array}{r} & 6.4432 \\ + &1.7000 \\ \hline & 8.1432 \end{array}$$
Now, subtracting 8.1432 from 9.2530
$$\begin{array}{r} & 9.2530 \\ - & 8.1432 \\ \hline & 1.1098 \end{array}$$
Hence, 8.57 - 6.4432 - 1.70 + 0.683 = 1.1098