` P = 1/(1.6) + 1/(6.11) + ................... + 1/(496.501)`
`5P = (6-1)/(1.6) + (11-6)/(6.11) + ...................... + (501-496)/(496.501)`
`5P = 1 - 1/6 + 1/6 - 1/11 + ............................ + 1/496 - 1/501`
`5P = 1 - 1/501 = 500/501`
`P = 500/501 : 5 = 100/501`
` M = 1/(1.2.3) + 1/(2.3.4) + .......................... + 1/(998.999.1000)`
`2M = (3-1)/(1.2.3) + (4-2)/(2.3.4) + ..................... + (1000 - 998)/(998.999.1000)`
`2M = 1/(1.2) - 1/(2.3) + 1/(2.3) - 1/(3.4) + ................. + 1/(998.999) - 1/(999.1000)`
`2M = 1/2 - 1/999000`
`M = (1/2 - 1/999000)/2`
` N = 1/(1.2.3) + 1/(2.3.4) + .......................... + 1/(98.99.100)`
`2N = (3-1)/(1.2.3) + (4-2)/(2.3.4) + ..................... + (100 - 98)/(98.99.100)`
`2N = 1/(1.2) - 1/(2.3) + 1/(2.3) - 1/(3.4) + ................. + 1/(98.99) - 1/(99.100)`
`2N = 1/2 - 1/9900`
`N = (1/2 - 1/9900)/2`
