Question

a blackboard of side 5m20cm and 3m40cm is to be painted. find the cost of painting it at the rate of Rs. 12 per sq.m

Answer 1

area of blackboard = 5.2 * 3.4 = 17.68m sq
rate of painting = Rs. 12 per m sq
cost of painting = 17.68 * 12 = 212.16 Rs.

Answer 2

first 
    cm to m
1cm=0.01m
20cm=0.2m
40cm=0.4m

length of blackboard=5.2m
breath of the black board=3.4m


now,
 area of blackboard=l*b
                               =5.2*3.4
                                =17.68m²

cost of painting=17.68m²*12
                         =212.16