24 men take 18 days to build a bridge. How many days will 6 men take to build the same bridge if all men work at the same rate. R5 000 is invested in a bank that offers simple interest per annum and accumulates to R11 750 in 9 years. Calculate the rate of interest.

To solve the first problem, we can use the concept of man-days. If 24 men take 18 days, that’s 24 x 18 = 432 man-days to complete the bridge. Now if only 6 men are working, the number of days they will take can be calculated by dividing the total man-days by the number of men: 432 ÷ 6 = 72 days. So, it will take 6 men 72 days to build the bridge. For the second question regarding simple interest, we use the formula: A = P(1 + rt), where A is the total amount, P is the principal, r is the rate, and t is the time (in years). Here, A = 11,750, P = 5,000, and t = 9 years. Rearranging, we find the rate: r = (A/P - 1) / t = (11,750/5,000 - 1) / 9. This simplifies to r = (2.35 - 1) / 9 = 0.149, or approximately 14.9% per annum as the interest rate.